scheme.c

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/* T I N Y S C H E M E    1 . 3 5
 *   Dimitrios Souflis (dsouflis@acm.org)
 *   Based on MiniScheme (original credits follow)
 * (MINISCM)               coded by Atsushi Moriwaki (11/5/1989)
 * (MINISCM)           E-MAIL :  moriwaki@kurims.kurims.kyoto-u.ac.jp
 * (MINISCM) This version has been modified by R.C. Secrist.
 * (MINISCM)
 * (MINISCM) Mini-Scheme is now maintained by Akira KIDA.
 * (MINISCM)
 * (MINISCM) This is a revised and modified version by Akira KIDA.
 * (MINISCM)  current version is 0.85k4 (15 May 1994)
 *
 */
 
#include <assert.h>
 
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
 
#define _SCHEME_SOURCE
#include "scheme-private.h"
#ifndef WIN32
#include <unistd.h>
#endif
#if USE_DL
#include "dynload.h"
#endif
#if USE_MATH
#include <math.h>
#endif
#include <limits.h>
#include <float.h>
#include <ctype.h>
#ifdef HAVE_UNISTD_H
#include <unistd.h> /* access() on Linux */
#endif
#include <stddef.h>
 
#if USE_STRCASECMP
#include <strings.h>
#define stricmp strcasecmp
#endif
 
/* Used for documentation purposes, to signal functions in 'interface' */
#define INTERFACE
 
#define TOK_EOF         (-1)
#define TOK_LPAREN      0
#define TOK_RPAREN      1
#define TOK_DOT         2
#define TOK_ATOM        3
#define TOK_QUOTE       4
#define TOK_COMMENT     5
#define TOK_DQUOTE      6
#define TOK_BQUOTE      7
#define TOK_COMMA       8
#define TOK_ATMARK      9
#define TOK_SHARP       10
#define TOK_SHARP_CONST 11
#define TOK_VEC         12
 
#define BACKQUOTE '`'
 
/*
 *  Basic memory allocation units
 */
 
#define banner "TinyScheme 1.35"
 
#ifdef HAVE_STRING_H
#include <string.h>
#endif
#include <stdlib.h>
#ifndef macintosh
#ifdef HAVE_MALLOC_H
#include <malloc.h>
#endif
#else
static int
stricmp(const char* s1, const char* s2) {
    unsigned char c1, c2;
    do {
        c1 = tolower(*s1);
        c2 = tolower(*s2);
        if (c1 < c2)
            return -1;
        else if (c1 > c2)
            return 1;
        s1++, s2++;
    } while (c1 != 0);
    return 0;
}
#endif /* macintosh */
 
#ifndef HAVE_STRLWR
static const char*
strlwr(char* s) {
    const char* p = s;
    while (*s) {
        *s = tolower((int)*s);
        s++;
    }
    return p;
}
#endif
 
#ifndef prompt
#define prompt "> "
#endif
 
#ifndef InitFile
#define InitFile "init.scm"
#endif
 
#ifndef FIRST_CELLSEGS
#define FIRST_CELLSEGS 3
#endif
 
enum scheme_types {
    T_STRING           = 1,
    T_NUMBER           = 2,
    T_SYMBOL           = 3,
    T_PROC             = 4,
    T_PAIR             = 5,
    T_CLOSURE          = 6,
    T_CONTINUATION     = 7,
    T_FOREIGN          = 8,
    T_CHARACTER        = 9,
    T_PORT             = 10,
    T_VECTOR           = 11,
    T_MACRO            = 12,
    T_PROMISE          = 13,
    T_ENVIRONMENT      = 14,
    T_LAST_SYSTEM_TYPE = 14
};
 
/* ADJ is enough slack to align cells in a TYPE_BITS-bit boundary */
#define ADJ         32
#define TYPE_BITS   5
#define T_MASKTYPE  31                           /* 0000000000011111 */
#define T_SYNTAX    4096                         /* 0001000000000000 */
#define T_IMMUTABLE 8192                         /* 0010000000000000 */
#define T_ATOM      16384 /* 0100000000000000 */ /* only for gc */
#define CLRATOM     49151 /* 1011111111111111 */ /* only for gc */
#define MARK        32768                        /* 1000000000000000 */
#define UNMARK      32767                        /* 0111111111111111 */
 
static num num_add(num a, num b);
static num num_mul(num a, num b);
static num num_div(num a, num b);
static num num_intdiv(num a, num b);
static num num_sub(num a, num b);
static num num_rem(num a, num b);
static num num_mod(num a, num b);
static int num_eq(num a, num b);
static int num_gt(num a, num b);
static int num_ge(num a, num b);
static int num_lt(num a, num b);
static int num_le(num a, num b);
 
#if USE_MATH
static double round_per_R5RS(double x);
#endif
static int is_zero_double(double x);
 
static num num_zero;
static num num_one;
 
/* macros for cell operations */
#define typeflag(p) ((p)->_flag)
#define type(p)     (typeflag(p) & T_MASKTYPE)
 
INTERFACE INLINE int
is_string(pointer p) {
    return (type(p) == T_STRING);
}
 
#define strvalue(p)  ((p)->_object._string._svalue)
#define strlength(p) ((p)->_object._string._length)
 
INTERFACE INLINE int
is_vector(pointer p) {
    return (type(p) == T_VECTOR);
}
 
INTERFACE static void    fill_vector(pointer vec, pointer obj);
INTERFACE static pointer vector_elem(pointer vec, int ielem);
INTERFACE static pointer set_vector_elem(pointer vec, int ielem, pointer a);
 
INTERFACE INLINE int
is_number(pointer p) {
    return (type(p) == T_NUMBER);
}
 
INTERFACE INLINE int
is_integer(pointer p) {
    return ((p)->_object._number.is_fixnum);
}
 
INTERFACE INLINE int
is_real(pointer p) {
    return (!(p)->_object._number.is_fixnum);
}
 
INTERFACE INLINE int
is_character(pointer p) {
    return (type(p) == T_CHARACTER);
}
 
INTERFACE INLINE char*
string_value(pointer p) {
    return strvalue(p);
}
 
INLINE num
nvalue(pointer p) {
    return ((p)->_object._number);
}
 
INTERFACE long
ivalue(pointer p) {
    return (is_integer(p) ? (p)->_object._number.value.ivalue : (long)(p)->_object._number.value.rvalue);
}
 
INTERFACE double
rvalue(pointer p) {
    return (!is_integer(p) ? (p)->_object._number.value.rvalue : (double)(p)->_object._number.value.ivalue);
}
 
#define ivalue_unchecked(p) ((p)->_object._number.value.ivalue)
#define rvalue_unchecked(p) ((p)->_object._number.value.rvalue)
#define set_integer(p)      (p)->_object._number.is_fixnum = 1;
#define set_real(p)         (p)->_object._number.is_fixnum = 0;
 
INTERFACE long
charvalue(pointer p) {
    return ivalue_unchecked(p);
}
 
INTERFACE INLINE int
is_port(pointer p) {
    return (type(p) == T_PORT);
}
 
#define is_inport(p)  (type(p) == T_PORT && p->_object._port->kind & port_input)
#define is_outport(p) (type(p) == T_PORT && p->_object._port->kind & port_output)
 
INTERFACE INLINE int
is_pair(pointer p) {
    return (type(p) == T_PAIR);
}
 
#define car(p) ((p)->_object._cons._car)
#define cdr(p) ((p)->_object._cons._cdr)
 
INTERFACE pointer
pair_car(pointer p) {
    return car(p);
}
 
INTERFACE pointer
pair_cdr(pointer p) {
    return cdr(p);
}
 
INTERFACE pointer
set_car(pointer p, pointer q) {
    return car(p) = q;
}
 
INTERFACE pointer
set_cdr(pointer p, pointer q) {
    return cdr(p) = q;
}
 
INTERFACE INLINE int
is_symbol(pointer p) {
    return (type(p) == T_SYMBOL);
}
 
INTERFACE INLINE char*
symname(pointer p) {
    return strvalue(car(p));
}
#if USE_PLIST
SCHEME_EXPORT INLINE int
hasprop(pointer p) {
    return (typeflag(p) & T_SYMBOL);
}
 
#define symprop(p) cdr(p)
#endif
 
INTERFACE INLINE int
is_syntax(pointer p) {
    return (typeflag(p) & T_SYNTAX);
}
 
INTERFACE INLINE int
is_proc(pointer p) {
    return (type(p) == T_PROC);
}
 
INTERFACE INLINE int
is_foreign(pointer p) {
    return (type(p) == T_FOREIGN);
}
 
INTERFACE INLINE char*
syntaxname(pointer p) {
    return strvalue(car(p));
}
 
#define procnum(p) ivalue(p)
static const char* procname(pointer x);
 
INTERFACE INLINE int
is_closure(pointer p) {
    return (type(p) == T_CLOSURE);
}
 
INTERFACE INLINE int
is_macro(pointer p) {
    return (type(p) == T_MACRO);
}
 
INTERFACE INLINE pointer
closure_code(pointer p) {
    return car(p);
}
 
INTERFACE INLINE pointer
closure_env(pointer p) {
    return cdr(p);
}
 
INTERFACE INLINE int
is_continuation(pointer p) {
    return (type(p) == T_CONTINUATION);
}
 
#define cont_dump(p) cdr(p)
 
/* To do: promise should be forced ONCE only */
INTERFACE INLINE int
is_promise(pointer p) {
    return (type(p) == T_PROMISE);
}
 
INTERFACE INLINE int
is_environment(pointer p) {
    return (type(p) == T_ENVIRONMENT);
}
 
#define setenvironment(p) typeflag(p) = T_ENVIRONMENT
 
#define is_atom(p) (typeflag(p) & T_ATOM)
#define setatom(p) typeflag(p) |= T_ATOM
#define clratom(p) typeflag(p) &= CLRATOM
 
#define is_mark(p) (typeflag(p) & MARK)
#define setmark(p) typeflag(p) |= MARK
#define clrmark(p) typeflag(p) &= UNMARK
 
INTERFACE INLINE int
is_immutable(pointer p) {
    return (typeflag(p) & T_IMMUTABLE);
}
 
/*#define setimmutable(p)  typeflag(p) |= T_IMMUTABLE*/
INTERFACE INLINE void
setimmutable(pointer p) {
    typeflag(p) |= T_IMMUTABLE;
}
 
#define caar(p)   car(car(p))
#define cadr(p)   car(cdr(p))
#define cdar(p)   cdr(car(p))
#define cddr(p)   cdr(cdr(p))
#define cadar(p)  car(cdr(car(p)))
#define caddr(p)  car(cdr(cdr(p)))
#define cadaar(p) car(cdr(car(car(p))))
#define cadddr(p) car(cdr(cdr(cdr(p))))
#define cddddr(p) cdr(cdr(cdr(cdr(p))))
 
#if USE_CHAR_CLASSIFIERS
static INLINE int
Cisalpha(int c) {
    return isascii(c) && isalpha(c);
}
 
static INLINE int
Cisdigit(int c) {
    return isascii(c) && isdigit(c);
}
 
static INLINE int
Cisspace(int c) {
    return isascii(c) && isspace(c);
}
 
static INLINE int
Cisupper(int c) {
    return isascii(c) && isupper(c);
}
 
static INLINE int
Cislower(int c) {
    return isascii(c) && islower(c);
}
#endif
 
#if USE_ASCII_NAMES
static const char* charnames[32] = { "nul", "soh", "stx", "etx", "eot", "enq", "ack", "bel", "bs",  "ht",  "lf",
                                     "vt",  "ff",  "cr",  "so",  "si",  "dle", "dc1", "dc2", "dc3", "dc4", "nak",
                                     "syn", "etb", "can", "em",  "sub", "esc", "fs",  "gs",  "rs",  "us" };
 
static int
is_ascii_name(const char* name, int* pc) {
    int i;
    for (i = 0; i < 32; i++) {
        if (stricmp(name, charnames[i]) == 0) {
            *pc = i;
            return 1;
        }
    }
    if (stricmp(name, "del") == 0) {
        *pc = 127;
        return 1;
    }
    return 0;
}
 
#endif
 
static int            file_push(scheme* sc, const char* fname);
static void           file_pop(scheme* sc);
static int            file_interactive(scheme* sc);
static INLINE int     is_one_of(char* s, int c);
static int            alloc_cellseg(scheme* sc, int n);
static long           binary_decode(const char* s);
static INLINE pointer get_cell(scheme* sc, pointer a, pointer b);
static pointer        _get_cell(scheme* sc, pointer a, pointer b);
static pointer        get_consecutive_cells(scheme* sc, int n);
static pointer        find_consecutive_cells(scheme* sc, int n);
static void           finalize_cell(scheme* sc, pointer a);
static int            count_consecutive_cells(pointer x, int needed);
static pointer        find_slot_in_env(scheme* sc, pointer env, pointer sym, int all);
static pointer        mk_number(scheme* sc, num n);
static pointer        mk_empty_string(scheme* sc, int len, char fill);
static char*          store_string(scheme* sc, int len, const char* str, char fill);
static pointer        mk_vector(scheme* sc, int len);
static pointer        mk_atom(scheme* sc, char* q);
static pointer        mk_sharp_const(scheme* sc, char* name);
static pointer        mk_port(scheme* sc, port* p);
static pointer        port_from_filename(scheme* sc, const char* fn, int prop);
static pointer        port_from_file(scheme* sc, FILE*, int prop);
static pointer        port_from_string(scheme* sc, char* start, char* past_the_end, int prop);
static port*          port_rep_from_filename(scheme* sc, const char* fn, int prop);
static port*          port_rep_from_file(scheme* sc, FILE*, int prop);
static port*          port_rep_from_string(scheme* sc, char* start, char* past_the_end, int prop);
static void           port_close(scheme* sc, pointer p, int flag);
static void           mark(pointer a);
static void           gc(scheme* sc, pointer a, pointer b);
static int            basic_inchar(port* pt);
static int            inchar(scheme* sc);
static void           backchar(scheme* sc, int c);
static char*          readstr_upto(scheme* sc, char* delim);
static pointer        readstrexp(scheme* sc);
static INLINE void    skipspace(scheme* sc);
static int            token(scheme* sc);
static void           printslashstring(scheme* sc, char* s, int len);
static void           atom2str(scheme* sc, pointer l, int f, char** pp, int* plen);
static void           printatom(scheme* sc, pointer l, int f);
static pointer        mk_proc(scheme* sc, enum scheme_opcodes op);
static pointer        mk_closure(scheme* sc, pointer c, pointer e);
static pointer        mk_continuation(scheme* sc, pointer d);
static pointer        reverse(scheme* sc, pointer a);
static pointer        reverse_in_place(scheme* sc, pointer term, pointer list);
static pointer        append(scheme* sc, pointer a, pointer b);
static int            list_length(scheme* sc, pointer a);
static int            eqv(pointer a, pointer b);
static void           dump_stack_mark(scheme*);
static pointer        opexe_0(scheme* sc, enum scheme_opcodes op);
static pointer        opexe_1(scheme* sc, enum scheme_opcodes op);
static pointer        opexe_2(scheme* sc, enum scheme_opcodes op);
static pointer        opexe_3(scheme* sc, enum scheme_opcodes op);
static pointer        opexe_4(scheme* sc, enum scheme_opcodes op);
static pointer        opexe_5(scheme* sc, enum scheme_opcodes op);
static pointer        opexe_6(scheme* sc, enum scheme_opcodes op);
static void           Eval_Cycle(scheme* sc, enum scheme_opcodes op);
static void           assign_syntax(scheme* sc, char* name);
static int            syntaxnum(pointer p);
static void           assign_proc(scheme* sc, enum scheme_opcodes, char* name);
 
#define num_ivalue(n) (n.is_fixnum ? (n).value.ivalue : (long)(n).value.rvalue)
#define num_rvalue(n) (!n.is_fixnum ? (n).value.rvalue : (double)(n).value.ivalue)
 
static num
num_add(num a, num b) {
    num ret;
    ret.is_fixnum = a.is_fixnum && b.is_fixnum;
    if (ret.is_fixnum) {
        ret.value.ivalue = a.value.ivalue + b.value.ivalue;
    } else {
        ret.value.rvalue = num_rvalue(a) + num_rvalue(b);
    }
    return ret;
}
 
static num
num_mul(num a, num b) {
    num ret;
    ret.is_fixnum = a.is_fixnum && b.is_fixnum;
    if (ret.is_fixnum) {
        ret.value.ivalue = a.value.ivalue * b.value.ivalue;
    } else {
        ret.value.rvalue = num_rvalue(a) * num_rvalue(b);
    }
    return ret;
}
 
static num
num_div(num a, num b) {
    num ret;
    ret.is_fixnum = a.is_fixnum && b.is_fixnum && a.value.ivalue % b.value.ivalue == 0;
    if (ret.is_fixnum) {
        ret.value.ivalue = a.value.ivalue / b.value.ivalue;
    } else {
        ret.value.rvalue = num_rvalue(a) / num_rvalue(b);
    }
    return ret;
}
 
static num
num_intdiv(num a, num b) {
    num ret;
    ret.is_fixnum = a.is_fixnum && b.is_fixnum;
    if (ret.is_fixnum) {
        ret.value.ivalue = a.value.ivalue / b.value.ivalue;
    } else {
        ret.value.rvalue = num_rvalue(a) / num_rvalue(b);
    }
    return ret;
}
 
static num
num_sub(num a, num b) {
    num ret;
    ret.is_fixnum = a.is_fixnum && b.is_fixnum;
    if (ret.is_fixnum) {
        ret.value.ivalue = a.value.ivalue - b.value.ivalue;
    } else {
        ret.value.rvalue = num_rvalue(a) - num_rvalue(b);
    }
    return ret;
}
 
static num
num_rem(num a, num b) {
    num  ret;
    long e1, e2, res;
    ret.is_fixnum = a.is_fixnum && b.is_fixnum;
    e1            = num_ivalue(a);
    e2            = num_ivalue(b);
    res           = e1 % e2;
    /* modulo should have same sign as second operand */
    if (res > 0) {
        if (e1 < 0) {
            res -= labs(e2);
        }
    } else if (res < 0) {
        if (e1 > 0) {
            res += labs(e2);
        }
    }
    ret.value.ivalue = res;
    return ret;
}
 
static num
num_mod(num a, num b) {
    num  ret;
    long e1, e2, res;
    ret.is_fixnum = a.is_fixnum && b.is_fixnum;
    e1            = num_ivalue(a);
    e2            = num_ivalue(b);
    res           = e1 % e2;
    if (res * e2 < 0) { /* modulo should have same sign as second operand */
        e2 = labs(e2);
        if (res > 0) {
            res -= e2;
        } else {
            res += e2;
        }
    }
    ret.value.ivalue = res;
    return ret;
}
 
static int
num_eq(num a, num b) {
    int ret;
    int is_fixnum = a.is_fixnum && b.is_fixnum;
    if (is_fixnum) {
        ret = a.value.ivalue == b.value.ivalue;
    } else {
        ret = num_rvalue(a) == num_rvalue(b);
    }
    return ret;
}
 
static int
num_gt(num a, num b) {
    int ret;
    int is_fixnum = a.is_fixnum && b.is_fixnum;
    if (is_fixnum) {
        ret = a.value.ivalue > b.value.ivalue;
    } else {
        ret = num_rvalue(a) > num_rvalue(b);
    }
    return ret;
}
 
static int
num_ge(num a, num b) {
    return !num_lt(a, b);
}
 
static int
num_lt(num a, num b) {
    int ret;
    int is_fixnum = a.is_fixnum && b.is_fixnum;
    if (is_fixnum) {
        ret = a.value.ivalue < b.value.ivalue;
    } else {
        ret = num_rvalue(a) < num_rvalue(b);
    }
    return ret;
}
 
static int
num_le(num a, num b) {
    return !num_gt(a, b);
}
 
#if USE_MATH
/* Round to nearest. Round to even if midway */
static double
round_per_R5RS(double x) {
    double fl  = floor(x);
    double ce  = ceil(x);
    double dfl = x - fl;
    double dce = ce - x;
    if (dfl > dce) {
        return ce;
    } else if (dfl < dce) {
        return fl;
    } else {
        if (fmod(fl, 2.0) == 0.0) { /* I imagine this holds */
            return fl;
        } else {
            return ce;
        }
    }
}
#endif
 
static int
is_zero_double(double x) {
    return x < DBL_MIN && x > -DBL_MIN;
}
 
static long
binary_decode(const char* s) {
    long x = 0;
 
    while (*s != 0 && (*s == '1' || *s == '0')) {
        x <<= 1;
        x += *s - '0';
        s++;
    }
 
    return x;
}
 
/* allocate new cell segment */
static int
alloc_cellseg(scheme* sc, int n) {
    pointer newp;
    pointer last;
    pointer p;
    char*   cp;
    long    i;
    int     k;
    size_t  adj = ADJ;
 
    if (adj < sizeof(struct cell)) {
        adj = sizeof(struct cell);
    }
 
    for (k = 0; k < n; k++) {
        if (sc->last_cell_seg >= CELL_NSEGMENT - 1)
            return k;
        cp = (char*)sc->malloc(CELL_SEGSIZE * sizeof(struct cell) + adj);
        if (cp == 0)
            return k;
        i                = ++sc->last_cell_seg;
        sc->alloc_seg[i] = cp;
        /* adjust in TYPE_BITS-bit boundary */
        /* Check that the casting below is safe. */
        static_assert(sizeof(size_t) == sizeof(cp), "Can't cast pointer to size_t.");
        if ((size_t)cp % adj != 0) {
            cp = (char*)(adj * ((size_t)cp / adj + 1));
        }
        /* insert new segment in address order */
        newp            = (pointer)cp;
        sc->cell_seg[i] = newp;
        while (i > 0 && sc->cell_seg[i - 1] > sc->cell_seg[i]) {
            p                 = sc->cell_seg[i];
            sc->cell_seg[i]   = sc->cell_seg[i - 1];
            sc->cell_seg[--i] = p;
        }
        sc->fcells += CELL_SEGSIZE;
        last = newp + CELL_SEGSIZE - 1;
        for (p = newp; p <= last; p++) {
            typeflag(p) = 0;
            cdr(p)      = p + 1;
            car(p)      = sc->NIL;
        }
        /* insert new cells in address order on free list */
        if (sc->free_cell == sc->NIL || p < sc->free_cell) {
            cdr(last)     = sc->free_cell;
            sc->free_cell = newp;
        } else {
            p = sc->free_cell;
            while (cdr(p) != sc->NIL && newp > cdr(p))
                p = cdr(p);
            cdr(last) = cdr(p);
            cdr(p)    = newp;
        }
    }
    return n;
}
 
static INLINE pointer
get_cell(scheme* sc, pointer a, pointer b) {
    if (sc->free_cell != sc->NIL) {
        pointer x     = sc->free_cell;
        sc->free_cell = cdr(x);
        --sc->fcells;
        return (x);
    }
    return _get_cell(sc, a, b);
}
 
/* get new cell.  parameter a, b is marked by gc. */
static pointer
_get_cell(scheme* sc, pointer a, pointer b) {
    pointer x;
 
    if (sc->no_memory) {
        return sc->sink;
    }
 
    if (sc->free_cell == sc->NIL) {
        gc(sc, a, b);
        if (sc->fcells < sc->last_cell_seg * 8 || sc->free_cell == sc->NIL) {
            /* if only a few recovered, get more to avoid fruitless gc's */
            if (!alloc_cellseg(sc, 1) && sc->free_cell == sc->NIL) {
                sc->no_memory = 1;
                return sc->sink;
            }
        }
    }
    x             = sc->free_cell;
    sc->free_cell = cdr(x);
    --sc->fcells;
    return (x);
}
 
static pointer
get_consecutive_cells(scheme* sc, int n) {
    pointer x;
 
    if (sc->no_memory) {
        return sc->sink;
    }
 
    /* Are there any cells available? */
    x = find_consecutive_cells(sc, n);
    if (x == sc->NIL) {
        /* If not, try gc'ing some */
        gc(sc, sc->NIL, sc->NIL);
        x = find_consecutive_cells(sc, n);
        if (x == sc->NIL) {
            /* If there still aren't, try getting more heap */
            if (!alloc_cellseg(sc, 1)) {
                sc->no_memory = 1;
                return sc->sink;
            }
        }
        x = find_consecutive_cells(sc, n);
        if (x == sc->NIL) {
            /* If all fail, report failure */
            sc->no_memory = 1;
            return sc->sink;
        }
    }
    return (x);
}
 
static int
count_consecutive_cells(pointer x, int needed) {
    int n = 1;
    while (cdr(x) == x + 1) {
        x = cdr(x);
        n++;
        if (n > needed)
            return n;
    }
    return n;
}
 
static pointer
find_consecutive_cells(scheme* sc, int n) {
    pointer* pp;
    int      cnt;
 
    pp = &sc->free_cell;
    while (*pp != sc->NIL) {
        cnt = count_consecutive_cells(*pp, n);
        if (cnt >= n) {
            pointer x = *pp;
            *pp       = cdr(*pp + n - 1);
            sc->fcells -= n;
            return x;
        }
        pp = &cdr(*pp + cnt - 1);
    }
    return sc->NIL;
}
 
/* get new cons cell */
pointer
_cons(scheme* sc, pointer a, pointer b, int immutable) {
    pointer x = get_cell(sc, a, b);
 
    typeflag(x) = T_PAIR;
    if (immutable) {
        setimmutable(x);
    }
    car(x) = a;
    cdr(x) = b;
    return (x);
}
 
/* ========== oblist implementation  ========== */
 
#ifndef USE_OBJECT_LIST
 
static int hash_fn(const char* key, int table_size);
 
static pointer
oblist_initial_value(scheme* sc) {
    return mk_vector(sc, 461); /* probably should be bigger */
}
 
/* returns the new symbol */
static pointer
oblist_add_by_name(scheme* sc, const char* name) {
    pointer x;
    int     location;
 
    x           = immutable_cons(sc, mk_string(sc, name), sc->NIL);
    typeflag(x) = T_SYMBOL;
    setimmutable(car(x));
 
    location = hash_fn(name, ivalue_unchecked(sc->oblist));
    set_vector_elem(sc->oblist, location, immutable_cons(sc, x, vector_elem(sc->oblist, location)));
    return x;
}
 
static INLINE pointer
oblist_find_by_name(scheme* sc, const char* name) {
    int     location;
    pointer x;
    char*   s;
 
    location = hash_fn(name, ivalue_unchecked(sc->oblist));
    for (x = vector_elem(sc->oblist, location); x != sc->NIL; x = cdr(x)) {
        s = symname(car(x));
        /* case-insensitive, per R5RS section 2. */
        if (stricmp(name, s) == 0) {
            return car(x);
        }
    }
    return sc->NIL;
}
 
static pointer
oblist_all_symbols(scheme* sc) {
    int     i;
    pointer x;
    pointer ob_list = sc->NIL;
 
    for (i = 0; i < ivalue_unchecked(sc->oblist); i++) {
        for (x = vector_elem(sc->oblist, i); x != sc->NIL; x = cdr(x)) {
            ob_list = cons(sc, x, ob_list);
        }
    }
    return ob_list;
}
 
#else
 
static pointer
oblist_initial_value(scheme* sc) {
    return sc->NIL;
}
 
static INLINE pointer
oblist_find_by_name(scheme* sc, const char* name) {
    pointer x;
    char*   s;
 
    for (x = sc->oblist; x != sc->NIL; x = cdr(x)) {
        s = symname(car(x));
        /* case-insensitive, per R5RS section 2. */
        if (stricmp(name, s) == 0) {
            return car(x);
        }
    }
    return sc->NIL;
}
 
/* returns the new symbol */
static pointer
oblist_add_by_name(scheme* sc, const char* name) {
    pointer x;
 
    x           = immutable_cons(sc, mk_string(sc, name), sc->NIL);
    typeflag(x) = T_SYMBOL;
    setimmutable(car(x));
    sc->oblist = immutable_cons(sc, x, sc->oblist);
    return x;
}
 
static pointer
oblist_all_symbols(scheme* sc) {
    return sc->oblist;
}
 
#endif
 
static pointer
mk_port(scheme* sc, port* p) {
    pointer x = get_cell(sc, sc->NIL, sc->NIL);
 
    typeflag(x)      = T_PORT | T_ATOM;
    x->_object._port = p;
    return (x);
}
 
pointer
mk_foreign_func(scheme* sc, foreign_func f) {
    pointer x = get_cell(sc, sc->NIL, sc->NIL);
 
    typeflag(x)    = (T_FOREIGN | T_ATOM);
    x->_object._ff = f;
    return (x);
}
 
INTERFACE pointer
mk_character(scheme* sc, int c) {
    pointer x = get_cell(sc, sc->NIL, sc->NIL);
 
    typeflag(x)         = (T_CHARACTER | T_ATOM);
    ivalue_unchecked(x) = c;
    set_integer(x);
    return (x);
}
 
/* get number atom (integer) */
INTERFACE pointer
mk_integer(scheme* sc, long num) {
    pointer x = get_cell(sc, sc->NIL, sc->NIL);
 
    typeflag(x)         = (T_NUMBER | T_ATOM);
    ivalue_unchecked(x) = num;
    set_integer(x);
    return (x);
}
 
INTERFACE pointer
mk_real(scheme* sc, double n) {
    pointer x = get_cell(sc, sc->NIL, sc->NIL);
 
    typeflag(x)         = (T_NUMBER | T_ATOM);
    rvalue_unchecked(x) = n;
    set_real(x);
    return (x);
}
 
static pointer
mk_number(scheme* sc, num n) {
    if (n.is_fixnum) {
        return mk_integer(sc, n.value.ivalue);
    } else {
        return mk_real(sc, n.value.rvalue);
    }
}
 
/* allocate name to string area */
static char*
store_string(scheme* sc, int len_str, const char* str, char fill) {
    char* q;
 
    q = (char*)sc->malloc(len_str + 1);
    if (q == 0) {
        sc->no_memory = 1;
        return sc->strbuff;
    }
    if (str != 0) {
        strcpy(q, str);
    } else {
        memset(q, fill, len_str);
        q[len_str] = 0;
    }
    return (q);
}
 
/* get new string */
INTERFACE pointer
mk_string(scheme* sc, const char* str) {
    return mk_counted_string(sc, str, strlen(str));
}
 
INTERFACE pointer
mk_counted_string(scheme* sc, const char* str, int len) {
    pointer x = get_cell(sc, sc->NIL, sc->NIL);
 
    strvalue(x)  = store_string(sc, len, str, 0);
    typeflag(x)  = (T_STRING | T_ATOM);
    strlength(x) = len;
    return (x);
}
 
static pointer
mk_empty_string(scheme* sc, int len, char fill) {
    pointer x = get_cell(sc, sc->NIL, sc->NIL);
 
    strvalue(x)  = store_string(sc, len, 0, fill);
    typeflag(x)  = (T_STRING | T_ATOM);
    strlength(x) = len;
    return (x);
}
 
INTERFACE static pointer
mk_vector(scheme* sc, int len) {
    pointer x           = get_consecutive_cells(sc, len / 2 + len % 2 + 1);
    typeflag(x)         = (T_VECTOR | T_ATOM);
    ivalue_unchecked(x) = len;
    set_integer(x);
    fill_vector(x, sc->NIL);
    return x;
}
 
INTERFACE static void
fill_vector(pointer vec, pointer obj) {
    int i;
    int num = ivalue(vec) / 2 + ivalue(vec) % 2;
    for (i = 0; i < num; i++) {
        typeflag(vec + 1 + i) = T_PAIR;
        setimmutable(vec + 1 + i);
        car(vec + 1 + i) = obj;
        cdr(vec + 1 + i) = obj;
    }
}
 
INTERFACE static pointer
vector_elem(pointer vec, int ielem) {
    int n = ielem / 2;
    if (ielem % 2 == 0) {
        return car(vec + 1 + n);
    } else {
        return cdr(vec + 1 + n);
    }
}
 
INTERFACE static pointer
set_vector_elem(pointer vec, int ielem, pointer a) {
    int n = ielem / 2;
    if (ielem % 2 == 0) {
        return car(vec + 1 + n) = a;
    } else {
        return cdr(vec + 1 + n) = a;
    }
}
 
/* get new symbol */
INTERFACE pointer
mk_symbol(scheme* sc, const char* name) {
    pointer x;
 
    /* first check oblist */
    x = oblist_find_by_name(sc, name);
    if (x != sc->NIL) {
        return (x);
    } else {
        x = oblist_add_by_name(sc, name);
        return (x);
    }
}
 
INTERFACE pointer
gensym(scheme* sc) {
    pointer x;
    char    name[40];
 
    for (; sc->gensym_cnt < LONG_MAX; sc->gensym_cnt++) {
        sprintf(name, "gensym-%ld", sc->gensym_cnt);
 
        /* first check oblist */
        x = oblist_find_by_name(sc, name);
 
        if (x != sc->NIL) {
            continue;
        } else {
            x = oblist_add_by_name(sc, name);
            return (x);
        }
    }
 
    return sc->NIL;
}
 
/* make symbol or number atom from string */
static pointer
mk_atom(scheme* sc, char* q) {
    char c, *p;
    int  has_dec_point = 0;
    int  has_fp_exp    = 0;
 
#if USE_COLON_HOOK
    if ((p = strstr(q, "::")) != 0) {
        *p = 0;
        return cons(
            sc, sc->COLON_HOOK,
            cons(
                sc, cons(sc, sc->QUOTE, cons(sc, mk_atom(sc, p + 2), sc->NIL)),
                cons(sc, mk_symbol(sc, strlwr(q)), sc->NIL)
            )
        );
    }
#endif
 
    p = q;
    c = *p++;
    if ((c == '+') || (c == '-')) {
        c = *p++;
        if (c == '.') {
            has_dec_point = 1;
            c             = *p++;
        }
        if (!isdigit((int)c)) {
            return (mk_symbol(sc, strlwr(q)));
        }
    } else if (c == '.') {
        has_dec_point = 1;
        c             = *p++;
        if (!isdigit((int)c)) {
            return (mk_symbol(sc, strlwr(q)));
        }
    } else if (!isdigit((int)c)) {
        return (mk_symbol(sc, strlwr(q)));
    }
 
    for (; (c = *p) != 0; ++p) {
        if (!isdigit((int)c)) {
            if (c == '.') {
                if (!has_dec_point) {
                    has_dec_point = 1;
                    continue;
                }
            } else if ((c == 'e') || (c == 'E')) {
                if (!has_fp_exp) {
                    has_dec_point = 1; /* decimal point illegal
                                          from now on */
                    p++;
                    if ((*p == '-') || (*p == '+') || isdigit((int)*p)) {
                        continue;
                    }
                }
            }
            return (mk_symbol(sc, strlwr(q)));
        }
    }
    if (has_dec_point) {
        return mk_real(sc, atof(q));
    }
    return (mk_integer(sc, atol(q)));
}
 
/* make constant */
static pointer
mk_sharp_const(scheme* sc, char* name) {
    long x;
    char tmp[256];
 
    if (!strcmp(name, "t"))
        return (sc->T);
    else if (!strcmp(name, "f"))
        return (sc->F);
    else if (*name == 'o') { /* #o (octal) */
        sprintf(tmp, "0%s", name + 1);
        sscanf(tmp, "%lo", &x);
        return (mk_integer(sc, x));
    } else if (*name == 'd') { /* #d (decimal) */
        sscanf(name + 1, "%ld", &x);
        return (mk_integer(sc, x));
    } else if (*name == 'x') { /* #x (hex) */
        sprintf(tmp, "0x%s", name + 1);
        sscanf(tmp, "%lx", &x);
        return (mk_integer(sc, x));
    } else if (*name == 'b') { /* #b (binary) */
        x = binary_decode(name + 1);
        return (mk_integer(sc, x));
    } else if (*name == '\\') { /* #\w (character) */
        int c = 0;
        if (stricmp(name + 1, "space") == 0) {
            c = ' ';
        } else if (stricmp(name + 1, "newline") == 0) {
            c = '\n';
        } else if (stricmp(name + 1, "return") == 0) {
            c = '\r';
        } else if (stricmp(name + 1, "tab") == 0) {
            c = '\t';
        } else if (name[1] == 'x' && name[2] != 0) {
            int c1 = 0;
            if (sscanf(name + 2, "%x", &c1) == 1 && c1 < 256) {
                c = c1;
            } else {
                return sc->NIL;
            }
#if USE_ASCII_NAMES
        } else if (is_ascii_name(name + 1, &c)) {
            /* nothing */
#endif
        } else if (name[2] == 0) {
            c = name[1];
        } else {
            return sc->NIL;
        }
        return mk_character(sc, c);
    } else
        return (sc->NIL);
}
 
/* ========== garbage collector ========== */
 
/*--
 *  We use algorithm E (Knuth, The Art of Computer Programming Vol.1,
 *  sec. 2.3.5), the Schorr-Deutsch-Waite link-inversion algorithm,
 *  for marking.
 */
static void
mark(pointer a) {
    pointer t, q, p;
 
    t = (pointer)0;
    p = a;
E2:
    setmark(p);
    if (is_vector(p)) {
        int i;
        int num = ivalue_unchecked(p) / 2 + ivalue_unchecked(p) % 2;
        for (i = 0; i < num; i++) {
            /* Vector cells will be treated like ordinary cells */
            mark(p + 1 + i);
        }
    }
    if (is_atom(p))
        goto E6;
    /* E4: down car */
    q = car(p);
    if (q && !is_mark(q)) {
        setatom(p); /* a note that we have moved car */
        car(p) = t;
        t      = p;
        p      = q;
        goto E2;
    }
E5:
    q = cdr(p); /* down cdr */
    if (q && !is_mark(q)) {
        cdr(p) = t;
        t      = p;
        p      = q;
        goto E2;
    }
E6: /* up.  Undo the link switching from steps E4 and E5. */
    if (!t)
        return;
    q = t;
    if (is_atom(q)) {
        clratom(q);
        t      = car(q);
        car(q) = p;
        p      = q;
        goto E5;
    } else {
        t      = cdr(q);
        cdr(q) = p;
        p      = q;
        goto E6;
    }
}
 
/* garbage collection. parameter a, b is marked. */
static void
gc(scheme* sc, pointer a, pointer b) {
    pointer p;
    int     i;
 
    if (sc->gc_verbose) {
        putstr(sc, "gc...");
    }
 
    /* mark system globals */
    mark(sc->oblist);
    mark(sc->global_env);
 
    /* mark current registers */
    mark(sc->args);
    mark(sc->envir);
    mark(sc->code);
    dump_stack_mark(sc);
    mark(sc->value);
    mark(sc->inport);
    mark(sc->save_inport);
    mark(sc->outport);
    mark(sc->loadport);
 
    /* mark variables a, b */
    mark(a);
    mark(b);
 
    /* garbage collect */
    clrmark(sc->NIL);
    sc->fcells    = 0;
    sc->free_cell = sc->NIL;
    /* free-list is kept sorted by address so as to maintain consecutive
       ranges, if possible, for use with vectors. Here we scan the cells
       (which are also kept sorted by address) downwards to build the
       free-list in sorted order.
    */
    for (i = sc->last_cell_seg; i >= 0; i--) {
        p = sc->cell_seg[i] + CELL_SEGSIZE;
        while (--p >= sc->cell_seg[i]) {
            if (is_mark(p)) {
                clrmark(p);
            } else {
                /* reclaim cell */
                if (typeflag(p) != 0) {
                    finalize_cell(sc, p);
                    typeflag(p) = 0;
                    car(p)      = sc->NIL;
                }
                ++sc->fcells;
                cdr(p)        = sc->free_cell;
                sc->free_cell = p;
            }
        }
    }
 
    if (sc->gc_verbose) {
        char msg[80];
        sprintf(msg, "done: %ld cells were recovered.\n", sc->fcells);
        putstr(sc, msg);
    }
}
 
static void
finalize_cell(scheme* sc, pointer a) {
    if (is_string(a)) {
        sc->free(strvalue(a));
    } else if (is_port(a)) {
        if (a->_object._port->kind & port_file && a->_object._port->rep.stdio.closeit) {
            port_close(sc, a, port_input | port_output);
        }
        sc->free(a->_object._port);
    }
}
 
/* ========== Routines for Reading ========== */
 
static int
file_push(scheme* sc, const char* fname) {
    FILE* fin = fopen(fname, "r");
    if (fin != 0) {
        sc->file_i++;
        sc->load_stack[sc->file_i].kind              = port_file | port_input;
        sc->load_stack[sc->file_i].rep.stdio.file    = fin;
        sc->load_stack[sc->file_i].rep.stdio.closeit = 1;
        sc->nesting_stack[sc->file_i]                = 0;
        sc->loadport->_object._port                  = sc->load_stack + sc->file_i;
    }
    return fin != 0;
}
 
static void
file_pop(scheme* sc) {
    sc->nesting = sc->nesting_stack[sc->file_i];
    if (sc->file_i != 0) {
        port_close(sc, sc->loadport, port_input);
        sc->file_i--;
        sc->loadport->_object._port = sc->load_stack + sc->file_i;
        if (file_interactive(sc)) {
            putstr(sc, prompt);
        }
    }
}
 
static int
file_interactive(scheme* sc) {
    return sc->file_i == 0 && sc->load_stack[0].rep.stdio.file == stdin && sc->inport->_object._port->kind & port_file;
}
 
static port*
port_rep_from_filename(scheme* sc, const char* fn, int prop) {
    FILE* f;
    char* rw;
    port* pt;
    if (prop == (port_input | port_output)) {
        rw = "a+";
    } else if (prop == port_output) {
        rw = "w";
    } else {
        rw = "r";
    }
    f = fopen(fn, rw);
    if (f == 0) {
        return 0;
    }
    pt                    = port_rep_from_file(sc, f, prop);
    pt->rep.stdio.closeit = 1;
    return pt;
}
 
static pointer
port_from_filename(scheme* sc, const char* fn, int prop) {
    port* pt;
    pt = port_rep_from_filename(sc, fn, prop);
    if (pt == 0) {
        return sc->NIL;
    }
    return mk_port(sc, pt);
}
 
static port*
port_rep_from_file(scheme* sc, FILE* f, int prop) {
    /*char *rw;*/
    port* pt;
    pt = (port*)sc->malloc(sizeof(port));
    if (pt == 0) {
        return 0;
    }
    /*
    if(prop==(port_input|port_output)) {
      rw="a+";
    } else if(prop==port_output) {
      rw="w";
    } else {
      rw="r";
    }
    */
    pt->kind              = port_file | prop;
    pt->rep.stdio.file    = f;
    pt->rep.stdio.closeit = 0;
    return pt;
}
 
static pointer
port_from_file(scheme* sc, FILE* f, int prop) {
    port* pt;
    pt = port_rep_from_file(sc, f, prop);
    if (pt == 0) {
        return sc->NIL;
    }
    return mk_port(sc, pt);
}
 
static port*
port_rep_from_string(scheme* sc, char* start, char* past_the_end, int prop) {
    port* pt;
    pt = (port*)sc->malloc(sizeof(port));
    if (pt == 0) {
        return 0;
    }
    pt->kind                    = port_string | prop;
    pt->rep.string.start        = start;
    pt->rep.string.curr         = start;
    pt->rep.string.past_the_end = past_the_end;
    return pt;
}
 
static pointer
port_from_string(scheme* sc, char* start, char* past_the_end, int prop) {
    port* pt;
    pt = port_rep_from_string(sc, start, past_the_end, prop);
    if (pt == 0) {
        return sc->NIL;
    }
    return mk_port(sc, pt);
}
 
static void
port_close(scheme* sc, pointer p, int flag) {
    port* pt = p->_object._port;
    pt->kind &= ~flag;
    if ((pt->kind & (port_input | port_output)) == 0) {
        if (pt->kind & port_file) {
            fclose(pt->rep.stdio.file);
        }
        pt->kind = port_free;
    }
}
 
/* get new character from input file */
static int
inchar(scheme* sc) {
    int   c;
    port* pt;
again:
    pt = sc->inport->_object._port;
    c  = basic_inchar(pt);
    if (c == EOF && sc->inport == sc->loadport && sc->file_i != 0) {
        file_pop(sc);
        if (sc->nesting != 0) {
            return EOF;
        }
        goto again;
    }
    return c;
}
 
static int
basic_inchar(port* pt) {
    if (pt->kind & port_file) {
        return fgetc(pt->rep.stdio.file);
    } else {
        if (*pt->rep.string.curr == 0 || pt->rep.string.curr == pt->rep.string.past_the_end) {
            return EOF;
        } else {
            return *pt->rep.string.curr++;
        }
    }
}
 
/* back character to input buffer */
static void
backchar(scheme* sc, int c) {
    port* pt;
    if (c == EOF)
        return;
    pt = sc->inport->_object._port;
    if (pt->kind & port_file) {
        ungetc(c, pt->rep.stdio.file);
    } else {
        if (pt->rep.string.curr != pt->rep.string.start) {
            --pt->rep.string.curr;
        }
    }
}
 
INTERFACE void
putstr(scheme* sc, const char* s) {
    port* pt = sc->outport->_object._port;
    if (pt->kind & port_file) {
        fputs(s, pt->rep.stdio.file);
    } else {
        for (; *s; s++) {
            if (pt->rep.string.curr != pt->rep.string.past_the_end) {
                *pt->rep.string.curr++ = *s;
            }
        }
    }
}
 
static void
putchars(scheme* sc, const char* s, int len) {
    port* pt = sc->outport->_object._port;
    if (pt->kind & port_file) {
        /* use the return value here to eliminate a compiler warning */
        if (fwrite(s, 1, len, pt->rep.stdio.file) == 0)
            return;
    } else {
        for (; len; len--) {
            if (pt->rep.string.curr != pt->rep.string.past_the_end) {
                *pt->rep.string.curr++ = *s++;
            }
        }
    }
}
 
INTERFACE void
putcharacter(scheme* sc, int c) {
    port* pt = sc->outport->_object._port;
    if (pt->kind & port_file) {
        fputc(c, pt->rep.stdio.file);
    } else {
        if (pt->rep.string.curr != pt->rep.string.past_the_end) {
            *pt->rep.string.curr++ = c;
        }
    }
}
 
/* read characters up to delimiter, but cater to character constants */
static char*
readstr_upto(scheme* sc, char* delim) {
    char* p = sc->strbuff;
 
    while (!is_one_of(delim, (*p++ = inchar(sc))))
        ;
    if (p == sc->strbuff + 2 && p[-2] == '\\') {
        *p = 0;
    } else {
        backchar(sc, p[-1]);
        *--p = '\0';
    }
    return sc->strbuff;
}
 
/* read string expression "xxx...xxx" */
static pointer
readstrexp(scheme* sc) {
    char* p = sc->strbuff;
    int   c;
    int   c1 = 0;
 
    enum {
        st_ok,
        st_bsl,
        st_x1,
        st_x2
    } state = st_ok;
 
    for (;;) {
        c = inchar(sc);
        if (c == EOF || p - sc->strbuff > sizeof(sc->strbuff) - 1) {
            return sc->F;
        }
        switch (state) {
            case st_ok:
                switch (c) {
                    case '\\': state = st_bsl; break;
                    case '"': *p = 0; return mk_counted_string(sc, sc->strbuff, p - sc->strbuff);
                    default: *p++ = c; break;
                }
                break;
            case st_bsl:
                switch (c) {
                    case 'x':
                    case 'X':
                        state = st_x1;
                        c1    = 0;
                        break;
                    case 'n':
                        *p++  = '\n';
                        state = st_ok;
                        break;
                    case 't':
                        *p++  = '\t';
                        state = st_ok;
                        break;
                    case 'r':
                        *p++  = '\r';
                        state = st_ok;
                        break;
                    case '"':
                        *p++  = '"';
                        state = st_ok;
                        break;
                    default:
                        *p++  = c;
                        state = st_ok;
                        break;
                }
                break;
            case st_x1:
            case st_x2:
                c = toupper(c);
                if (c >= '0' && c <= 'F') {
                    if (c <= '9') {
                        c1 = (c1 << 4) + c - '0';
                    } else {
                        c1 = (c1 << 4) + c - 'A' + 10;
                    }
                    if (state == st_x1) {
                        state = st_x2;
                    } else {
                        *p++  = c1;
                        state = st_ok;
                    }
                } else {
                    return sc->F;
                }
                break;
        }
    }
}
 
/* check c is in chars */
static INLINE int
is_one_of(char* s, int c) {
    if (c == EOF)
        return 1;
    while (*s)
        if (*s++ == c)
            return (1);
    return (0);
}
 
/* skip white characters */
static INLINE void
skipspace(scheme* sc) {
    int c;
    while (isspace(c = inchar(sc)))
        ;
    if (c != EOF) {
        backchar(sc, c);
    }
}
 
/* get token */
static int
token(scheme* sc) {
    int c;
    skipspace(sc);
    switch (c = inchar(sc)) {
        case EOF: return (TOK_EOF);
        case '(': return (TOK_LPAREN);
        case ')': return (TOK_RPAREN);
        case '.':
            c = inchar(sc);
            if (is_one_of(" \n\t", c)) {
                return (TOK_DOT);
            } else {
                backchar(sc, c);
                backchar(sc, '.');
                return TOK_ATOM;
            }
        case '\'': return (TOK_QUOTE);
        case ';': return (TOK_COMMENT);
        case '"': return (TOK_DQUOTE);
        case BACKQUOTE: return (TOK_BQUOTE);
        case ',':
            if ((c = inchar(sc)) == '@')
                return (TOK_ATMARK);
            else {
                backchar(sc, c);
                return (TOK_COMMA);
            }
        case '#':
            c = inchar(sc);
            if (c == '(') {
                return (TOK_VEC);
            } else if (c == '!') {
                return TOK_COMMENT;
            } else {
                backchar(sc, c);
                if (is_one_of(" tfodxb\\", c)) {
                    return TOK_SHARP_CONST;
                } else {
                    return (TOK_SHARP);
                }
            }
        default: backchar(sc, c); return (TOK_ATOM);
    }
}
 
/* ========== Routines for Printing ========== */
#define ok_abbrev(x) (is_pair(x) && cdr(x) == sc->NIL)
 
static void
printslashstring(scheme* sc, char* p, int len) {
    int            i;
    unsigned char* s = (unsigned char*)p;
    putcharacter(sc, '"');
    for (i = 0; i < len; i++) {
        if (*s == 0xff || *s == '"' || *s < ' ' || *s == '\\') {
            putcharacter(sc, '\\');
            switch (*s) {
                case '"': putcharacter(sc, '"'); break;
                case '\n': putcharacter(sc, 'n'); break;
                case '\t': putcharacter(sc, 't'); break;
                case '\r': putcharacter(sc, 'r'); break;
                case '\\': putcharacter(sc, '\\'); break;
                default:
                    {
                        int d = *s / 16;
                        putcharacter(sc, 'x');
                        if (d < 10) {
                            putcharacter(sc, d + '0');
                        } else {
                            putcharacter(sc, d - 10 + 'A');
                        }
                        d = *s % 16;
                        if (d < 10) {
                            putcharacter(sc, d + '0');
                        } else {
                            putcharacter(sc, d - 10 + 'A');
                        }
                    }
            }
        } else {
            putcharacter(sc, *s);
        }
        s++;
    }
    putcharacter(sc, '"');
}
 
/* print atoms */
static void
printatom(scheme* sc, pointer l, int f) {
    char* p;
    int   len;
    atom2str(sc, l, f, &p, &len);
    putchars(sc, p, len);
}
 
/* Uses internal buffer unless string pointer is already available */
static void
atom2str(scheme* sc, pointer l, int f, char** pp, int* plen) {
    char* p;
 
    if (l == sc->NIL) {
        p = "()";
    } else if (l == sc->T) {
        p = "#t";
    } else if (l == sc->F) {
        p = "#f";
    } else if (l == sc->EOF_OBJ) {
        p = "#<EOF>";
    } else if (is_port(l)) {
        p = sc->strbuff;
        strcpy(p, "#<PORT>");
    } else if (is_number(l)) {
        p = sc->strbuff;
        if (is_integer(l)) {
            sprintf(p, "%ld", ivalue_unchecked(l));
        } else {
            sprintf(p, "%.10g", rvalue_unchecked(l));
        }
    } else if (is_string(l)) {
        if (!f) {
            p = strvalue(l);
        } else { /* Hack, uses the fact that printing is needed */
            *pp   = sc->strbuff;
            *plen = 0;
            printslashstring(sc, strvalue(l), strlength(l));
            return;
        }
    } else if (is_character(l)) {
        int c = charvalue(l);
        p     = sc->strbuff;
        if (!f) {
            p[0] = c;
            p[1] = 0;
        } else {
            switch (c) {
                case ' ': sprintf(p, "#\\space"); break;
                case '\n': sprintf(p, "#\\newline"); break;
                case '\r': sprintf(p, "#\\return"); break;
                case '\t': sprintf(p, "#\\tab"); break;
                default:
#if USE_ASCII_NAMES
                    if (c == 127) {
                        strcpy(p, "#\\del");
                        break;
                    } else if (c < 32) {
                        strcpy(p, "#\\");
                        strcat(p, charnames[c]);
                        break;
                    }
#else
                    if (c < 32) {
                        sprintf(p, "#\\x%x", c);
                        break;
                    }
#endif
                    sprintf(p, "#\\%c", c);
                    break;
            }
        }
    } else if (is_symbol(l)) {
        p = symname(l);
    } else if (is_proc(l)) {
        p = sc->strbuff;
        sprintf(p, "#<%s PROCEDURE %ld>", procname(l), procnum(l));
    } else if (is_macro(l)) {
        p = "#<MACRO>";
    } else if (is_closure(l)) {
        p = "#<CLOSURE>";
    } else if (is_promise(l)) {
        p = "#<PROMISE>";
    } else if (is_foreign(l)) {
        p = sc->strbuff;
        sprintf(p, "#<FOREIGN PROCEDURE %ld>", procnum(l));
    } else if (is_continuation(l)) {
        p = "#<CONTINUATION>";
    } else {
        p = "#<ERROR>";
    }
    *pp   = p;
    *plen = strlen(p);
}
 
/* ========== Routines for Evaluation Cycle ========== */
 
/* make closure. c is code. e is environment */
static pointer
mk_closure(scheme* sc, pointer c, pointer e) {
    pointer x = get_cell(sc, c, e);
 
    typeflag(x) = T_CLOSURE;
    car(x)      = c;
    cdr(x)      = e;
    return (x);
}
 
/* make continuation. */
static pointer
mk_continuation(scheme* sc, pointer d) {
    pointer x = get_cell(sc, sc->NIL, d);
 
    typeflag(x)  = T_CONTINUATION;
    cont_dump(x) = d;
    return (x);
}
 
static pointer
list_star(scheme* sc, pointer d) {
    pointer p, q;
    if (cdr(d) == sc->NIL) {
        return car(d);
    }
    p = cons(sc, car(d), cdr(d));
    q = p;
    while (cdr(cdr(p)) != sc->NIL) {
        d = cons(sc, car(p), cdr(p));
        if (cdr(cdr(p)) != sc->NIL) {
            p = cdr(d);
        }
    }
    cdr(p) = car(cdr(p));
    return q;
}
 
/* reverse list -- produce new list */
static pointer
reverse(scheme* sc, pointer a) {
    /* a must be checked by gc */
    pointer p = sc->NIL;
 
    for (; is_pair(a); a = cdr(a)) {
        p = cons(sc, car(a), p);
    }
    return (p);
}
 
/* reverse list --- in-place */
static pointer
reverse_in_place(scheme* sc, pointer term, pointer list) {
    pointer p = list, result = term, q;
 
    while (p != sc->NIL) {
        q      = cdr(p);
        cdr(p) = result;
        result = p;
        p      = q;
    }
    return (result);
}
 
/* append list -- produce new list */
static pointer
append(scheme* sc, pointer a, pointer b) {
    pointer p = b, q;
 
    if (a != sc->NIL) {
        a = reverse(sc, a);
        while (a != sc->NIL) {
            q      = cdr(a);
            cdr(a) = p;
            p      = a;
            a      = q;
        }
    }
    return (p);
}
 
/* equivalence of atoms */
static int
eqv(pointer a, pointer b) {
    if (is_string(a)) {
        if (is_string(b))
            return (strvalue(a) == strvalue(b));
        else
            return (0);
    } else if (is_number(a)) {
        if (is_number(b))
            return num_eq(nvalue(a), nvalue(b));
        else
            return (0);
    } else if (is_character(a)) {
        if (is_character(b))
            return charvalue(a) == charvalue(b);
        else
            return (0);
    } else if (is_port(a)) {
        if (is_port(b))
            return a == b;
        else
            return (0);
    } else if (is_proc(a)) {
        if (is_proc(b))
            return procnum(a) == procnum(b);
        else
            return (0);
    } else {
        return (a == b);
    }
}
 
/* true or false value macro */
/* () is #t in R5RS */
#define is_true(p)  ((p) != sc->F)
#define is_false(p) ((p) == sc->F)
 
/* ========== Environment implementation  ========== */
 
#if !defined(USE_ALIST_ENV) || !defined(USE_OBJECT_LIST)
 
static int
hash_fn(const char* key, int table_size) {
    unsigned int hashed = 0;
    const char*  c;
    int          bits_per_int = sizeof(unsigned int) * 8;
 
    for (c = key; *c; c++) {
        /* letters have about 5 bits in them */
        hashed = (hashed << 5) | (hashed >> (bits_per_int - 5));
        hashed ^= *c;
    }
    return hashed % table_size;
}
#endif
 
#ifndef USE_ALIST_ENV
 
/*
 * In this implementation, each frame of the environment may be
 * a hash table: a vector of alists hashed by variable name.
 * In practice, we use a vector only for the initial frame;
 * subsequent frames are too small and transient for the lookup
 * speed to out-weigh the cost of making a new vector.
 */
 
static void
new_frame_in_env(scheme* sc, pointer old_env) {
    pointer new_frame;
 
    /* The interaction-environment has about 300 variables in it. */
    if (old_env == sc->NIL) {
        new_frame = mk_vector(sc, 461);
    } else {
        new_frame = sc->NIL;
    }
 
    sc->envir = immutable_cons(sc, new_frame, old_env);
    setenvironment(sc->envir);
}
 
static INLINE void
new_slot_spec_in_env(scheme* sc, pointer env, pointer variable, pointer value) {
    pointer slot = immutable_cons(sc, variable, value);
 
    if (is_vector(car(env))) {
        int location = hash_fn(symname(variable), ivalue_unchecked(car(env)));
 
        set_vector_elem(car(env), location, immutable_cons(sc, slot, vector_elem(car(env), location)));
    } else {
        car(env) = immutable_cons(sc, slot, car(env));
    }
}
 
static pointer
find_slot_in_env(scheme* sc, pointer env, pointer hdl, int all) {
    pointer x = sc->NIL, y = sc->NIL;
    int     location = 0;
 
    for (x = env; x != sc->NIL; x = cdr(x)) {
        if (is_vector(car(x))) {
            location = hash_fn(symname(hdl), ivalue_unchecked(car(x)));
            y        = vector_elem(car(x), location);
        } else {
            y = car(x);
        }
        for (; y != sc->NIL; y = cdr(y)) {
            if (caar(y) == hdl) {
                break;
            }
        }
        if (y != sc->NIL) {
            break;
        }
        if (!all) {
            return sc->NIL;
        }
    }
    if (x != sc->NIL) {
        return car(y);
    }
    return sc->NIL;
}
 
#else /* USE_ALIST_ENV */
 
static INLINE void
new_frame_in_env(scheme* sc, pointer old_env) {
    sc->envir = immutable_cons(sc, sc->NIL, old_env);
    setenvironment(sc->envir);
}
 
static INLINE void
new_slot_spec_in_env(scheme* sc, pointer env, pointer variable, pointer value) {
    car(env) = immutable_cons(sc, immutable_cons(sc, variable, value), car(env));
}
 
static pointer
find_slot_in_env(scheme* sc, pointer env, pointer hdl, int all) {
    pointer x, y;
    for (x = env; x != sc->NIL; x = cdr(x)) {
        for (y = car(x); y != sc->NIL; y = cdr(y)) {
            if (caar(y) == hdl) {
                break;
            }
        }
        if (y != sc->NIL) {
            break;
        }
        if (!all) {
            return sc->NIL;
        }
    }
    if (x != sc->NIL) {
        return car(y);
    }
    return sc->NIL;
}
 
#endif /* USE_ALIST_ENV else */
 
static INLINE void
new_slot_in_env(scheme* sc, pointer variable, pointer value) {
    new_slot_spec_in_env(sc, sc->envir, variable, value);
}
 
static INLINE void
set_slot_in_env(scheme* sc, pointer slot, pointer value) {
    cdr(slot) = value;
}
 
static INLINE pointer
slot_value_in_env(pointer slot) {
    return cdr(slot);
}
 
/* ========== Evaluation Cycle ========== */
 
static pointer
_Error_1(scheme* sc, const char* s, pointer a) {
#if USE_ERROR_HOOK
    pointer x;
    pointer hdl = sc->ERROR_HOOK;
 
    x = find_slot_in_env(sc, sc->envir, hdl, 1);
    if (x != sc->NIL) {
        if (a != 0) {
            sc->code = cons(sc, cons(sc, sc->QUOTE, cons(sc, (a), sc->NIL)), sc->NIL);
        } else {
            sc->code = sc->NIL;
        }
        sc->code = cons(sc, mk_string(sc, (s)), sc->code);
        setimmutable(car(sc->code));
        sc->code = cons(sc, slot_value_in_env(x), sc->code);
        sc->op   = (int)OP_EVAL;
        return sc->T;
    }
#endif
 
    if (a != 0) {
        sc->args = cons(sc, (a), sc->NIL);
    } else {
        sc->args = sc->NIL;
    }
    sc->args = cons(sc, mk_string(sc, (s)), sc->args);
    setimmutable(car(sc->args));
    sc->op = (int)OP_ERR0;
    return sc->T;
}
 
#define Error_1(sc, s, a) return _Error_1(sc, s, a)
#define Error_0(sc, s)    return _Error_1(sc, s, 0)
 
/* Too small to turn into function */
#define BEGIN do {
#define END \
    }       \
    while (0)
#define s_goto(sc, a)  \
    BEGIN              \
    sc->op = (int)(a); \
    return sc->T;      \
    END
 
#define s_return(sc, a) return _s_return(sc, a)
 
#ifndef USE_SCHEME_STACK
 
/* this structure holds all the interpreter's registers */
struct dump_stack_frame {
    enum scheme_opcodes op;
    pointer             args;
    pointer             envir;
    pointer             code;
};
 
#define STACK_GROWTH 3
 
static void
s_save(scheme* sc, enum scheme_opcodes op, pointer args, pointer code) {
    long                     nframes = (long)sc->dump;
    struct dump_stack_frame* next_frame;
 
    /* enough room for the next frame? */
    if (nframes >= sc->dump_size) {
        sc->dump_size += STACK_GROWTH;
        /* alas there is no sc->realloc */
        sc->dump_base = realloc(sc->dump_base, sizeof(struct dump_stack_frame) * sc->dump_size);
    }
    next_frame        = (struct dump_stack_frame*)sc->dump_base + nframes;
    next_frame->op    = op;
    next_frame->args  = args;
    next_frame->envir = sc->envir;
    next_frame->code  = code;
    sc->dump          = (pointer)(nframes + 1L);
}
 
static pointer
_s_return(scheme* sc, pointer a) {
    long                     nframes = (long)sc->dump;
    struct dump_stack_frame* frame;
 
    sc->value = (a);
    if (nframes <= 0) {
        return sc->NIL;
    }
    nframes--;
    frame     = (struct dump_stack_frame*)sc->dump_base + nframes;
    sc->op    = frame->op;
    sc->args  = frame->args;
    sc->envir = frame->envir;
    sc->code  = frame->code;
    sc->dump  = (pointer)nframes;
    return sc->T;
}
 
static INLINE void
dump_stack_reset(scheme* sc) {
    /* in this implementation, sc->dump is the number of frames on the stack */
    sc->dump = (pointer)0;
}
 
static INLINE void
dump_stack_initialize(scheme* sc) {
    sc->dump_size = 0;
    sc->dump_base = NULL;
    dump_stack_reset(sc);
}
 
static void
dump_stack_free(scheme* sc) {
    free(sc->dump_base);
    sc->dump_base = NULL;
    sc->dump      = (pointer)0;
    sc->dump_size = 0;
}
 
static INLINE void
dump_stack_mark(scheme* sc) {
    long nframes = (long)sc->dump;
    int  i;
    for (i = 0; i < nframes; i++) {
        struct dump_stack_frame* frame;
        frame = (struct dump_stack_frame*)sc->dump_base + i;
        mark(frame->args);
        mark(frame->envir);
        mark(frame->code);
    }
}
 
#else
 
static INLINE void
dump_stack_reset(scheme* sc) {
    sc->dump = sc->NIL;
}
 
static INLINE void
dump_stack_initialize(scheme* sc) {
    dump_stack_reset(sc);
}
 
static void
dump_stack_free(scheme* sc) {
    sc->dump = sc->NIL;
}
 
static pointer
_s_return(scheme* sc, pointer a) {
    sc->value = (a);
    if (sc->dump == sc->NIL)
        return sc->NIL;
    sc->op    = ivalue(car(sc->dump));
    sc->args  = cadr(sc->dump);
    sc->envir = caddr(sc->dump);
    sc->code  = cadddr(sc->dump);
    sc->dump  = cddddr(sc->dump);
    return sc->T;
}
 
static void
s_save(scheme* sc, enum scheme_opcodes op, pointer args, pointer code) {
    sc->dump = cons(sc, sc->envir, cons(sc, (code), sc->dump));
    sc->dump = cons(sc, (args), sc->dump);
    sc->dump = cons(sc, mk_integer(sc, (long)(op)), sc->dump);
}
 
static INLINE void
dump_stack_mark(scheme* sc) {
    mark(sc->dump);
}
#endif
 
#define s_retbool(tf) s_return(sc, (tf) ? sc->T : sc->F)
 
static pointer
opexe_0(scheme* sc, enum scheme_opcodes op) {
    pointer x, y;
 
    switch (op) {
        case OP_LOAD: /* load */
            if (file_interactive(sc)) {
                fprintf(sc->outport->_object._port->rep.stdio.file, "Loading %s\n", strvalue(car(sc->args)));
            }
            if (!file_push(sc, strvalue(car(sc->args)))) {
                Error_1(sc, "unable to open", car(sc->args));
            }
            s_goto(sc, OP_T0LVL);
 
        case OP_T0LVL: /* top level */
            if (file_interactive(sc)) {
                putstr(sc, "\n");
            }
            sc->nesting = 0;
            dump_stack_reset(sc);
            sc->envir       = sc->global_env;
            sc->save_inport = sc->inport;
            sc->inport      = sc->loadport;
            s_save(sc, OP_T0LVL, sc->NIL, sc->NIL);
            s_save(sc, OP_VALUEPRINT, sc->NIL, sc->NIL);
            s_save(sc, OP_T1LVL, sc->NIL, sc->NIL);
            if (file_interactive(sc)) {
                putstr(sc, prompt);
            }
            s_goto(sc, OP_READ_INTERNAL);
 
        case OP_T1LVL: /* top level */
            sc->code   = sc->value;
            sc->inport = sc->save_inport;
            s_goto(sc, OP_EVAL);
 
        case OP_READ_INTERNAL: /* internal read */
            sc->tok = token(sc);
            if (sc->tok == TOK_EOF) {
                if (sc->inport == sc->loadport) {
                    sc->args = sc->NIL;
                    s_goto(sc, OP_QUIT);
                } else {
                    s_return(sc, sc->EOF_OBJ);
                }
            }
            s_goto(sc, OP_RDSEXPR);
 
        case OP_GENSYM: s_return(sc, gensym(sc));
 
        case OP_VALUEPRINT: /* print evaluation result */
                            /* OP_VALUEPRINT is always pushed, because when changing from
                               non-interactive to interactive mode, it needs to be
                               already on the stack */
            if (sc->tracing) {
                putstr(sc, "\nGives: ");
            }
            if (file_interactive(sc)) {
                sc->print_flag = 1;
                sc->args       = sc->value;
                s_goto(sc, OP_P0LIST);
            } else {
                s_return(sc, sc->value);
            }
 
        case OP_EVAL: /* main part of evaluation */
#if USE_TRACING
            if (sc->tracing) {
                /*s_save(sc,OP_VALUEPRINT,sc->NIL,sc->NIL);*/
                s_save(sc, OP_REAL_EVAL, sc->args, sc->code);
                sc->args = sc->code;
                putstr(sc, "\nEval: ");
                s_goto(sc, OP_P0LIST);
            }
            /* fall through */
        case OP_REAL_EVAL:
#endif
            if (is_symbol(sc->code)) { /* symbol */
                x = find_slot_in_env(sc, sc->envir, sc->code, 1);
                if (x != sc->NIL) {
                    s_return(sc, slot_value_in_env(x));
                } else {
                    Error_1(sc, "eval: unbound variable:", sc->code);
                }
            } else if (is_pair(sc->code)) {
                if (is_syntax(x = car(sc->code))) { /* SYNTAX */
                    sc->code = cdr(sc->code);
                    s_goto(sc, syntaxnum(x));
                } else { /* first, eval top element and eval arguments */
                    s_save(sc, OP_E0ARGS, sc->NIL, sc->code);
                    /* If no macros => s_save(sc,OP_E1ARGS, sc->NIL, cdr(sc->code));*/
                    sc->code = car(sc->code);
                    s_goto(sc, OP_EVAL);
                }
            } else {
                s_return(sc, sc->code);
            }
 
        case OP_E0ARGS:                /* eval arguments */
            if (is_macro(sc->value)) { /* macro expansion */
                s_save(sc, OP_DOMACRO, sc->NIL, sc->NIL);
                sc->args = cons(sc, sc->code, sc->NIL);
                sc->code = sc->value;
                s_goto(sc, OP_APPLY);
            } else {
                sc->code = cdr(sc->code);
                s_goto(sc, OP_E1ARGS);
            }
 
        case OP_E1ARGS: /* eval arguments */
            sc->args = cons(sc, sc->value, sc->args);
            if (is_pair(sc->code)) { /* continue */
                s_save(sc, OP_E1ARGS, sc->args, cdr(sc->code));
                sc->code = car(sc->code);
                sc->args = sc->NIL;
                s_goto(sc, OP_EVAL);
            } else { /* end */
                sc->args = reverse_in_place(sc, sc->NIL, sc->args);
                sc->code = car(sc->args);
                sc->args = cdr(sc->args);
                s_goto(sc, OP_APPLY);
            }
 
#if USE_TRACING
        case OP_TRACING:
            {
                int tr      = sc->tracing;
                sc->tracing = ivalue(car(sc->args));
                s_return(sc, mk_integer(sc, tr));
            }
#endif
 
        case OP_APPLY: /* apply 'code' to 'args' */
#if USE_TRACING
            if (sc->tracing) {
                s_save(sc, OP_REAL_APPLY, sc->args, sc->code);
                sc->print_flag = 1;
                /*    sc->args=cons(sc,sc->code,sc->args);*/
                putstr(sc, "\nApply to: ");
                s_goto(sc, OP_P0LIST);
            }
            /* fall through */
        case OP_REAL_APPLY:
#endif
            if (is_proc(sc->code)) {
                s_goto(sc, procnum(sc->code)); /* PROCEDURE */
            } else if (is_foreign(sc->code)) {
                x = sc->code->_object._ff(sc, sc->args);
                s_return(sc, x);
            } else if (is_closure(sc->code) || is_macro(sc->code) || is_promise(sc->code)) { /* CLOSURE */
                /* Should not accept promise */
                /* make environment */
                new_frame_in_env(sc, closure_env(sc->code));
                for (x = car(closure_code(sc->code)), y = sc->args; is_pair(x); x = cdr(x), y = cdr(y)) {
                    if (y == sc->NIL) {
                        Error_0(sc, "not enough arguments");
                    } else {
                        new_slot_in_env(sc, car(x), car(y));
                    }
                }
                if (x == sc->NIL) {
                    /*--
                     * if (y != sc->NIL) {
                     *   Error_0(sc,"too many arguments");
                     * }
                     */
                } else if (is_symbol(x))
                    new_slot_in_env(sc, x, y);
                else {
                    Error_1(sc, "syntax error in closure: not a symbol:", x);
                }
                sc->code = cdr(closure_code(sc->code));
                sc->args = sc->NIL;
                s_goto(sc, OP_BEGIN);
            } else if (is_continuation(sc->code)) { /* CONTINUATION */
                sc->dump = cont_dump(sc->code);
                s_return(sc, sc->args != sc->NIL ? car(sc->args) : sc->NIL);
            } else {
                Error_0(sc, "illegal function");
            }
 
        case OP_DOMACRO: /* do macro */ sc->code = sc->value; s_goto(sc, OP_EVAL);
 
        case OP_LAMBDA: /* lambda */ s_return(sc, mk_closure(sc, sc->code, sc->envir));
 
        case OP_MKCLOSURE: /* make-closure */
            x = car(sc->args);
            if (car(x) == sc->LAMBDA) {
                x = cdr(x);
            }
            if (cdr(sc->args) == sc->NIL) {
                y = sc->envir;
            } else {
                y = cadr(sc->args);
            }
            s_return(sc, mk_closure(sc, x, y));
 
        case OP_QUOTE: /* quote */ x = car(sc->code); s_return(sc, car(sc->code));
 
        case OP_DEF0: /* define */
            if (is_pair(car(sc->code))) {
                x        = caar(sc->code);
                sc->code = cons(sc, sc->LAMBDA, cons(sc, cdar(sc->code), cdr(sc->code)));
            } else {
                x        = car(sc->code);
                sc->code = cadr(sc->code);
            }
            if (!is_symbol(x)) {
                Error_0(sc, "variable is not a symbol");
            }
            s_save(sc, OP_DEF1, sc->NIL, x);
            s_goto(sc, OP_EVAL);
 
        case OP_DEF1: /* define */
            x = find_slot_in_env(sc, sc->envir, sc->code, 0);
            if (x != sc->NIL) {
                set_slot_in_env(sc, x, sc->value);
            } else {
                new_slot_in_env(sc, sc->code, sc->value);
            }
            s_return(sc, sc->code);
 
        case OP_DEFP: /* defined? */
            x = sc->envir;
            if (cdr(sc->args) != sc->NIL) {
                x = cadr(sc->args);
            }
            s_retbool(find_slot_in_env(sc, x, car(sc->args), 1) != sc->NIL);
 
        case OP_SET0: /* set! */
            s_save(sc, OP_SET1, sc->NIL, car(sc->code));
            sc->code = cadr(sc->code);
            s_goto(sc, OP_EVAL);
 
        case OP_SET1: /* set! */
            y = find_slot_in_env(sc, sc->envir, sc->code, 1);
            if (y != sc->NIL) {
                set_slot_in_env(sc, y, sc->value);
                s_return(sc, sc->value);
            } else {
                Error_1(sc, "set!: unbound variable:", sc->code);
            }
 
        case OP_BEGIN: /* begin */
            if (!is_pair(sc->code)) {
                s_return(sc, sc->code);
            }
            if (cdr(sc->code) != sc->NIL) {
                s_save(sc, OP_BEGIN, sc->NIL, cdr(sc->code));
            }
            sc->code = car(sc->code);
            s_goto(sc, OP_EVAL);
 
        case OP_IF0: /* if */
            s_save(sc, OP_IF1, sc->NIL, cdr(sc->code));
            sc->code = car(sc->code);
            s_goto(sc, OP_EVAL);
 
        case OP_IF1: /* if */
            if (is_true(sc->value))
                sc->code = car(sc->code);
            else
                sc->code = cadr(sc->code); /* (if #f 1) ==> () because
                                            * car(sc->NIL) = sc->NIL */
            s_goto(sc, OP_EVAL);
 
        case OP_LET0: /* let */
            sc->args  = sc->NIL;
            sc->value = sc->code;
            sc->code  = is_symbol(car(sc->code)) ? cadr(sc->code) : car(sc->code);
            s_goto(sc, OP_LET1);
 
        case OP_LET1: /* let (calculate parameters) */
            sc->args = cons(sc, sc->value, sc->args);
            if (is_pair(sc->code)) { /* continue */
                s_save(sc, OP_LET1, sc->args, cdr(sc->code));
                sc->code = cadar(sc->code);
                sc->args = sc->NIL;
                s_goto(sc, OP_EVAL);
            } else { /* end */
                sc->args = reverse_in_place(sc, sc->NIL, sc->args);
                sc->code = car(sc->args);
                sc->args = cdr(sc->args);
                s_goto(sc, OP_LET2);
            }
 
        case OP_LET2: /* let */
            new_frame_in_env(sc, sc->envir);
            for (x = is_symbol(car(sc->code)) ? cadr(sc->code) : car(sc->code), y = sc->args; y != sc->NIL;
                 x = cdr(x), y = cdr(y)) {
                new_slot_in_env(sc, caar(x), car(y));
            }
            if (is_symbol(car(sc->code))) { /* named let */
                for (x = cadr(sc->code), sc->args = sc->NIL; x != sc->NIL; x = cdr(x)) {
 
                    sc->args = cons(sc, caar(x), sc->args);
                }
                x = mk_closure(sc, cons(sc, reverse_in_place(sc, sc->NIL, sc->args), cddr(sc->code)), sc->envir);
                new_slot_in_env(sc, car(sc->code), x);
                sc->code = cddr(sc->code);
                sc->args = sc->NIL;
            } else {
                sc->code = cdr(sc->code);
                sc->args = sc->NIL;
            }
            s_goto(sc, OP_BEGIN);
 
        case OP_LET0AST: /* let* */
            if (car(sc->code) == sc->NIL) {
                new_frame_in_env(sc, sc->envir);
                sc->code = cdr(sc->code);
                s_goto(sc, OP_BEGIN);
            }
            s_save(sc, OP_LET1AST, cdr(sc->code), car(sc->code));
            sc->code = cadaar(sc->code);
            s_goto(sc, OP_EVAL);
 
        case OP_LET1AST: /* let* (make new frame) */ new_frame_in_env(sc, sc->envir); s_goto(sc, OP_LET2AST);
 
        case OP_LET2AST: /* let* (calculate parameters) */
            new_slot_in_env(sc, caar(sc->code), sc->value);
            sc->code = cdr(sc->code);
            if (is_pair(sc->code)) { /* continue */
                s_save(sc, OP_LET2AST, sc->args, sc->code);
                sc->code = cadar(sc->code);
                sc->args = sc->NIL;
                s_goto(sc, OP_EVAL);
            } else { /* end */
                sc->code = sc->args;
                sc->args = sc->NIL;
                s_goto(sc, OP_BEGIN);
            }
        default: sprintf(sc->strbuff, "%d: illegal operator", sc->op); Error_0(sc, sc->strbuff);
    }
    return sc->T;
}
 
static pointer
opexe_1(scheme* sc, enum scheme_opcodes op) {
    pointer x, y;
 
    switch (op) {
        case OP_LET0REC: /* letrec */
            new_frame_in_env(sc, sc->envir);
            sc->args  = sc->NIL;
            sc->value = sc->code;
            sc->code  = car(sc->code);
            s_goto(sc, OP_LET1REC);
 
        case OP_LET1REC: /* letrec (calculate parameters) */
            sc->args = cons(sc, sc->value, sc->args);
            if (is_pair(sc->code)) { /* continue */
                s_save(sc, OP_LET1REC, sc->args, cdr(sc->code));
                sc->code = cadar(sc->code);
                sc->args = sc->NIL;
                s_goto(sc, OP_EVAL);
            } else { /* end */
                sc->args = reverse_in_place(sc, sc->NIL, sc->args);
                sc->code = car(sc->args);
                sc->args = cdr(sc->args);
                s_goto(sc, OP_LET2REC);
            }
 
        case OP_LET2REC: /* letrec */
            for (x = car(sc->code), y = sc->args; y != sc->NIL; x = cdr(x), y = cdr(y)) {
                new_slot_in_env(sc, caar(x), car(y));
            }
            sc->code = cdr(sc->code);
            sc->args = sc->NIL;
            s_goto(sc, OP_BEGIN);
 
        case OP_COND0: /* cond */
            if (!is_pair(sc->code)) {
                Error_0(sc, "syntax error in cond");
            }
            s_save(sc, OP_COND1, sc->NIL, sc->code);
            sc->code = caar(sc->code);
            s_goto(sc, OP_EVAL);
 
        case OP_COND1: /* cond */
            if (is_true(sc->value)) {
                if ((sc->code = cdar(sc->code)) == sc->NIL) {
                    s_return(sc, sc->value);
                }
                if (car(sc->code) == sc->FEED_TO) {
                    if (!is_pair(cdr(sc->code))) {
                        Error_0(sc, "syntax error in cond");
                    }
                    x        = cons(sc, sc->QUOTE, cons(sc, sc->value, sc->NIL));
                    sc->code = cons(sc, cadr(sc->code), cons(sc, x, sc->NIL));
                    s_goto(sc, OP_EVAL);
                }
                s_goto(sc, OP_BEGIN);
            } else {
                if ((sc->code = cdr(sc->code)) == sc->NIL) {
                    s_return(sc, sc->NIL);
                } else {
                    s_save(sc, OP_COND1, sc->NIL, sc->code);
                    sc->code = caar(sc->code);
                    s_goto(sc, OP_EVAL);
                }
            }
 
        case OP_DELAY: /* delay */
            x           = mk_closure(sc, cons(sc, sc->NIL, sc->code), sc->envir);
            typeflag(x) = T_PROMISE;
            s_return(sc, x);
 
        case OP_AND0: /* and */
            if (sc->code == sc->NIL) {
                s_return(sc, sc->T);
            }
            s_save(sc, OP_AND1, sc->NIL, cdr(sc->code));
            sc->code = car(sc->code);
            s_goto(sc, OP_EVAL);
 
        case OP_AND1: /* and */
            if (is_false(sc->value)) {
                s_return(sc, sc->value);
            } else if (sc->code == sc->NIL) {
                s_return(sc, sc->value);
            } else {
                s_save(sc, OP_AND1, sc->NIL, cdr(sc->code));
                sc->code = car(sc->code);
                s_goto(sc, OP_EVAL);
            }
 
        case OP_OR0: /* or */
            if (sc->code == sc->NIL) {
                s_return(sc, sc->F);
            }
            s_save(sc, OP_OR1, sc->NIL, cdr(sc->code));
            sc->code = car(sc->code);
            s_goto(sc, OP_EVAL);
 
        case OP_OR1: /* or */
            if (is_true(sc->value)) {
                s_return(sc, sc->value);
            } else if (sc->code == sc->NIL) {
                s_return(sc, sc->value);
            } else {
                s_save(sc, OP_OR1, sc->NIL, cdr(sc->code));
                sc->code = car(sc->code);
                s_goto(sc, OP_EVAL);
            }
 
        case OP_C0STREAM: /* cons-stream */
            s_save(sc, OP_C1STREAM, sc->NIL, cdr(sc->code));
            sc->code = car(sc->code);
            s_goto(sc, OP_EVAL);
 
        case OP_C1STREAM:            /* cons-stream */
            sc->args    = sc->value; /* save sc->value to register sc->args for gc */
            x           = mk_closure(sc, cons(sc, sc->NIL, sc->code), sc->envir);
            typeflag(x) = T_PROMISE;
            s_return(sc, cons(sc, sc->args, x));
 
        case OP_MACRO0: /* macro */
            if (is_pair(car(sc->code))) {
                x        = caar(sc->code);
                sc->code = cons(sc, sc->LAMBDA, cons(sc, cdar(sc->code), cdr(sc->code)));
            } else {
                x        = car(sc->code);
                sc->code = cadr(sc->code);
            }
            if (!is_symbol(x)) {
                Error_0(sc, "variable is not a symbol");
            }
            s_save(sc, OP_MACRO1, sc->NIL, x);
            s_goto(sc, OP_EVAL);
 
        case OP_MACRO1: /* macro */
            typeflag(sc->value) = T_MACRO;
            x                   = find_slot_in_env(sc, sc->envir, sc->code, 0);
            if (x != sc->NIL) {
                set_slot_in_env(sc, x, sc->value);
            } else {
                new_slot_in_env(sc, sc->code, sc->value);
            }
            s_return(sc, sc->code);
 
        case OP_CASE0: /* case */
            s_save(sc, OP_CASE1, sc->NIL, cdr(sc->code));
            sc->code = car(sc->code);
            s_goto(sc, OP_EVAL);
 
        case OP_CASE1: /* case */
            for (x = sc->code; x != sc->NIL; x = cdr(x)) {
                if (!is_pair(y = caar(x))) {
                    break;
                }
                for (; y != sc->NIL; y = cdr(y)) {
                    if (eqv(car(y), sc->value)) {
                        break;
                    }
                }
                if (y != sc->NIL) {
                    break;
                }
            }
            if (x != sc->NIL) {
                if (is_pair(caar(x))) {
                    sc->code = cdar(x);
                    s_goto(sc, OP_BEGIN);
                } else { /* else */
                    s_save(sc, OP_CASE2, sc->NIL, cdar(x));
                    sc->code = caar(x);
                    s_goto(sc, OP_EVAL);
                }
            } else {
                s_return(sc, sc->NIL);
            }
 
        case OP_CASE2: /* case */
            if (is_true(sc->value)) {
                s_goto(sc, OP_BEGIN);
            } else {
                s_return(sc, sc->NIL);
            }
 
        case OP_PAPPLY: /* apply */
            sc->code = car(sc->args);
            sc->args = list_star(sc, cdr(sc->args));
            /*sc->args = cadr(sc->args);*/
            s_goto(sc, OP_APPLY);
 
        case OP_PEVAL: /* eval */
            if (cdr(sc->args) != sc->NIL) {
                sc->envir = cadr(sc->args);
            }
            sc->code = car(sc->args);
            s_goto(sc, OP_EVAL);
 
        case OP_CONTINUATION: /* call-with-current-continuation */
            sc->code = car(sc->args);
            sc->args = cons(sc, mk_continuation(sc, sc->dump), sc->NIL);
            s_goto(sc, OP_APPLY);
 
        default: sprintf(sc->strbuff, "%d: illegal operator", sc->op); Error_0(sc, sc->strbuff);
    }
    return sc->T;
}
 
static pointer
opexe_2(scheme* sc, enum scheme_opcodes op) {
    pointer x;
    num     v;
#if USE_MATH
    double dd;
#endif
 
    switch (op) {
#if USE_MATH
        case OP_INEX2EX: /* inexact->exact */
            x = car(sc->args);
            if (is_integer(x)) {
                s_return(sc, x);
            } else if (modf(rvalue_unchecked(x), &dd) == 0.0) {
                s_return(sc, mk_integer(sc, ivalue(x)));
            } else {
                Error_1(sc, "inexact->exact: not integral:", x);
            }
 
        case OP_EXP: x = car(sc->args); s_return(sc, mk_real(sc, exp(rvalue(x))));
 
        case OP_LOG: x = car(sc->args); s_return(sc, mk_real(sc, log(rvalue(x))));
 
        case OP_SIN: x = car(sc->args); s_return(sc, mk_real(sc, sin(rvalue(x))));
 
        case OP_COS: x = car(sc->args); s_return(sc, mk_real(sc, cos(rvalue(x))));
 
        case OP_TAN: x = car(sc->args); s_return(sc, mk_real(sc, tan(rvalue(x))));
 
        case OP_ASIN: x = car(sc->args); s_return(sc, mk_real(sc, asin(rvalue(x))));
 
        case OP_ACOS: x = car(sc->args); s_return(sc, mk_real(sc, acos(rvalue(x))));
 
        case OP_ATAN:
            x = car(sc->args);
            if (cdr(sc->args) == sc->NIL) {
                s_return(sc, mk_real(sc, atan(rvalue(x))));
            } else {
                pointer y = cadr(sc->args);
                s_return(sc, mk_real(sc, atan2(rvalue(x), rvalue(y))));
            }
 
        case OP_SQRT: x = car(sc->args); s_return(sc, mk_real(sc, sqrt(rvalue(x))));
 
        case OP_EXPT:
            x = car(sc->args);
            if (cdr(sc->args) == sc->NIL) {
                Error_0(sc, "expt: needs two arguments");
            } else {
                pointer y = cadr(sc->args);
                s_return(sc, mk_real(sc, pow(rvalue(x), rvalue(y))));
            }
 
        case OP_FLOOR: x = car(sc->args); s_return(sc, mk_real(sc, floor(rvalue(x))));
 
        case OP_CEILING: x = car(sc->args); s_return(sc, mk_real(sc, ceil(rvalue(x))));
 
        case OP_TRUNCATE:
            {
                double rvalue_of_x;
                x           = car(sc->args);
                rvalue_of_x = rvalue(x);
                if (rvalue_of_x > 0) {
                    s_return(sc, mk_real(sc, floor(rvalue_of_x)));
                } else {
                    s_return(sc, mk_real(sc, ceil(rvalue_of_x)));
                }
            }
 
        case OP_ROUND: x = car(sc->args); s_return(sc, mk_real(sc, round_per_R5RS(rvalue(x))));
#endif
 
        case OP_ADD: /* + */
            v = num_zero;
            for (x = sc->args; x != sc->NIL; x = cdr(x)) {
                v = num_add(v, nvalue(car(x)));
            }
            s_return(sc, mk_number(sc, v));
 
        case OP_MUL: /* * */
            v = num_one;
            for (x = sc->args; x != sc->NIL; x = cdr(x)) {
                v = num_mul(v, nvalue(car(x)));
            }
            s_return(sc, mk_number(sc, v));
 
        case OP_SUB: /* - */
            if (cdr(sc->args) == sc->NIL) {
                x = sc->args;
                v = num_zero;
            } else {
                x = cdr(sc->args);
                v = nvalue(car(sc->args));
            }
            for (; x != sc->NIL; x = cdr(x)) {
                v = num_sub(v, nvalue(car(x)));
            }
            s_return(sc, mk_number(sc, v));
 
        case OP_DIV: /* / */
            if (cdr(sc->args) == sc->NIL) {
                x = sc->args;
                v = num_one;
            } else {
                x = cdr(sc->args);
                v = nvalue(car(sc->args));
            }
            for (; x != sc->NIL; x = cdr(x)) {
                if (!is_zero_double(rvalue(car(x))))
                    v = num_div(v, nvalue(car(x)));
                else {
                    Error_0(sc, "/: division by zero");
                }
            }
            s_return(sc, mk_number(sc, v));
 
        case OP_INTDIV: /* quotient */
            if (cdr(sc->args) == sc->NIL) {
                x = sc->args;
                v = num_one;
            } else {
                x = cdr(sc->args);
                v = nvalue(car(sc->args));
            }
            for (; x != sc->NIL; x = cdr(x)) {
                if (ivalue(car(x)) != 0)
                    v = num_intdiv(v, nvalue(car(x)));
                else {
                    Error_0(sc, "quotient: division by zero");
                }
            }
            s_return(sc, mk_number(sc, v));
 
        case OP_REM: /* remainder */
            v = nvalue(car(sc->args));
            if (ivalue(cadr(sc->args)) != 0)
                v = num_rem(v, nvalue(cadr(sc->args)));
            else {
                Error_0(sc, "remainder: division by zero");
            }
            s_return(sc, mk_number(sc, v));
 
        case OP_MOD: /* modulo */
            v = nvalue(car(sc->args));
            if (ivalue(cadr(sc->args)) != 0)
                v = num_mod(v, nvalue(cadr(sc->args)));
            else {
                Error_0(sc, "modulo: division by zero");
            }
            s_return(sc, mk_number(sc, v));
 
        case OP_CAR: /* car */ s_return(sc, caar(sc->args));
 
        case OP_CDR: /* cdr */ s_return(sc, cdar(sc->args));
 
        case OP_CONS: /* cons */ cdr(sc->args) = cadr(sc->args); s_return(sc, sc->args);
 
        case OP_SETCAR: /* set-car! */
            if (!is_immutable(car(sc->args))) {
                caar(sc->args) = cadr(sc->args);
                s_return(sc, car(sc->args));
            } else {
                Error_0(sc, "set-car!: unable to alter immutable pair");
            }
 
        case OP_SETCDR: /* set-cdr! */
            if (!is_immutable(car(sc->args))) {
                cdar(sc->args) = cadr(sc->args);
                s_return(sc, car(sc->args));
            } else {
                Error_0(sc, "set-cdr!: unable to alter immutable pair");
            }
 
        case OP_CHAR2INT:
            { /* char->integer */
                char c;
                c = (char)ivalue(car(sc->args));
                s_return(sc, mk_integer(sc, (unsigned char)c));
            }
 
        case OP_INT2CHAR:
            { /* integer->char */
                unsigned char c;
                c = (unsigned char)ivalue(car(sc->args));
                s_return(sc, mk_character(sc, (char)c));
            }
 
        case OP_CHARUPCASE:
            {
                unsigned char c;
                c = (unsigned char)ivalue(car(sc->args));
                c = toupper(c);
                s_return(sc, mk_character(sc, (char)c));
            }
 
        case OP_CHARDNCASE:
            {
                unsigned char c;
                c = (unsigned char)ivalue(car(sc->args));
                c = tolower(c);
                s_return(sc, mk_character(sc, (char)c));
            }
 
        case OP_STR2SYM: /* string->symbol */ s_return(sc, mk_symbol(sc, strvalue(car(sc->args))));
 
        case OP_STR2ATOM: /* string->atom */
            {
                char* s = strvalue(car(sc->args));
                if (*s == '#') {
                    s_return(sc, mk_sharp_const(sc, s + 1));
                } else {
                    s_return(sc, mk_atom(sc, s));
                }
            }
 
        case OP_SYM2STR: /* symbol->string */
            x = mk_string(sc, symname(car(sc->args)));
            setimmutable(x);
            s_return(sc, x);
        case OP_ATOM2STR: /* atom->string */
            x = car(sc->args);
            if (is_number(x) || is_character(x) || is_string(x) || is_symbol(x)) {
                char* p;
                int   len;
                atom2str(sc, x, 0, &p, &len);
                s_return(sc, mk_counted_string(sc, p, len));
            } else {
                Error_1(sc, "atom->string: not an atom:", x);
            }
 
        case OP_MKSTRING:
            { /* make-string */
                int fill = ' ';
                int len;
 
                len = ivalue(car(sc->args));
 
                if (cdr(sc->args) != sc->NIL) {
                    fill = charvalue(cadr(sc->args));
                }
                s_return(sc, mk_empty_string(sc, len, (char)fill));
            }
 
        case OP_STRLEN: /* string-length */ s_return(sc, mk_integer(sc, strlength(car(sc->args))));
 
        case OP_STRREF:
            { /* string-ref */
                char* str;
                int   index;
 
                str = strvalue(car(sc->args));
 
                index = ivalue(cadr(sc->args));
 
                if (index >= strlength(car(sc->args))) {
                    Error_1(sc, "string-ref: out of bounds:", cadr(sc->args));
                }
 
                s_return(sc, mk_character(sc, ((unsigned char*)str)[index]));
            }
 
        case OP_STRSET:
            { /* string-set! */
                char* str;
                int   index;
                int   c;
 
                if (is_immutable(car(sc->args))) {
                    Error_1(sc, "string-set!: unable to alter immutable string:", car(sc->args));
                }
                str = strvalue(car(sc->args));
 
                index = ivalue(cadr(sc->args));
                if (index >= strlength(car(sc->args))) {
                    Error_1(sc, "string-set!: out of bounds:", cadr(sc->args));
                }
 
                c = charvalue(caddr(sc->args));
 
                str[index] = (char)c;
                s_return(sc, car(sc->args));
            }
 
        case OP_STRAPPEND:
            { /* string-append */
                /* in 1.29 string-append was in Scheme in init.scm but was too slow */
                int     len = 0;
                pointer newstr;
                char*   pos;
 
                /* compute needed length for new string */
                for (x = sc->args; x != sc->NIL; x = cdr(x)) {
                    len += strlength(car(x));
                }
                newstr = mk_empty_string(sc, len, ' ');
                /* store the contents of the argument strings into the new string */
                for (pos = strvalue(newstr), x = sc->args; x != sc->NIL; pos += strlength(car(x)), x = cdr(x)) {
                    memcpy(pos, strvalue(car(x)), strlength(car(x)));
                }
                s_return(sc, newstr);
            }
 
        case OP_SUBSTR:
            { /* substring */
                char* str;
                int   index0;
                int   index1;
                int   len;
 
                str = strvalue(car(sc->args));
 
                index0 = ivalue(cadr(sc->args));
 
                if (index0 > strlength(car(sc->args))) {
                    Error_1(sc, "substring: start out of bounds:", cadr(sc->args));
                }
 
                if (cddr(sc->args) != sc->NIL) {
                    index1 = ivalue(caddr(sc->args));
                    if (index1 > strlength(car(sc->args)) || index1 < index0) {
                        Error_1(sc, "substring: end out of bounds:", caddr(sc->args));
                    }
                } else {
                    index1 = strlength(car(sc->args));
                }
 
                len = index1 - index0;
                x   = mk_empty_string(sc, len, ' ');
                memcpy(strvalue(x), str + index0, len);
                strvalue(x)[len] = 0;
 
                s_return(sc, x);
            }
 
        case OP_VECTOR:
            { /* vector */
                int     i;
                pointer vec;
                int     len = list_length(sc, sc->args);
                if (len < 0) {
                    Error_1(sc, "vector: not a proper list:", sc->args);
                }
                vec = mk_vector(sc, len);
                for (x = sc->args, i = 0; is_pair(x); x = cdr(x), i++) {
                    set_vector_elem(vec, i, car(x));
                }
                s_return(sc, vec);
            }
 
        case OP_MKVECTOR:
            { /* make-vector */
                pointer fill = sc->NIL;
                int     len;
                pointer vec;
 
                len = ivalue(car(sc->args));
 
                if (cdr(sc->args) != sc->NIL) {
                    fill = cadr(sc->args);
                }
                vec = mk_vector(sc, len);
                if (fill != sc->NIL) {
                    fill_vector(vec, fill);
                }
                s_return(sc, vec);
            }
 
        case OP_VECLEN: /* vector-length */ s_return(sc, mk_integer(sc, ivalue(car(sc->args))));
 
        case OP_VECREF:
            { /* vector-ref */
                int index;
 
                index = ivalue(cadr(sc->args));
 
                if (index >= ivalue(car(sc->args))) {
                    Error_1(sc, "vector-ref: out of bounds:", cadr(sc->args));
                }
 
                s_return(sc, vector_elem(car(sc->args), index));
            }
 
        case OP_VECSET:
            { /* vector-set! */
                int index;
 
                if (is_immutable(car(sc->args))) {
                    Error_1(sc, "vector-set!: unable to alter immutable vector:", car(sc->args));
                }
 
                index = ivalue(cadr(sc->args));
                if (index >= ivalue(car(sc->args))) {
                    Error_1(sc, "vector-set!: out of bounds:", cadr(sc->args));
                }
 
                set_vector_elem(car(sc->args), index, caddr(sc->args));
                s_return(sc, car(sc->args));
            }
 
        default: sprintf(sc->strbuff, "%d: illegal operator", sc->op); Error_0(sc, sc->strbuff);
    }
    return sc->T;
}
 
static int
list_length(scheme* sc, pointer a) {
    int     v = 0;
    pointer x;
    for (x = a, v = 0; is_pair(x); x = cdr(x)) {
        ++v;
    }
    if (x == sc->NIL) {
        return v;
    }
    return -1;
}
 
static pointer
opexe_3(scheme* sc, enum scheme_opcodes op) {
    pointer x;
    num     v;
    int (*comp_func)(num, num) = 0;
 
    switch (op) {
        case OP_NOT: /* not */ s_retbool(is_false(car(sc->args)));
        case OP_BOOLP: /* boolean? */ s_retbool(car(sc->args) == sc->F || car(sc->args) == sc->T);
        case OP_EOFOBJP: /* boolean? */ s_retbool(car(sc->args) == sc->EOF_OBJ);
        case OP_NULLP: /* null? */ s_retbool(car(sc->args) == sc->NIL);
        case OP_NUMEQ: /* = */
        case OP_LESS:  /* < */
        case OP_GRE:   /* > */
        case OP_LEQ:   /* <= */
        case OP_GEQ:   /* >= */
            switch (op) {
                case OP_NUMEQ: comp_func = num_eq; break;
                case OP_LESS: comp_func = num_lt; break;
                case OP_GRE: comp_func = num_gt; break;
                case OP_LEQ: comp_func = num_le; break;
                case OP_GEQ: comp_func = num_ge; break;
                default:;
            }
            x = sc->args;
            v = nvalue(car(x));
            x = cdr(x);
 
            for (; x != sc->NIL; x = cdr(x)) {
                if (!comp_func(v, nvalue(car(x)))) {
                    s_retbool(0);
                }
                v = nvalue(car(x));
            }
            s_retbool(1);
        case OP_SYMBOLP: /* symbol? */ s_retbool(is_symbol(car(sc->args)));
        case OP_NUMBERP: /* number? */ s_retbool(is_number(car(sc->args)));
        case OP_STRINGP: /* string? */ s_retbool(is_string(car(sc->args)));
        case OP_INTEGERP: /* integer? */ s_retbool(is_integer(car(sc->args)));
        case OP_REALP: /* real? */ s_retbool(is_number(car(sc->args))); /* All numbers are real */
        case OP_CHARP: /* char? */ s_retbool(is_character(car(sc->args)));
#if USE_CHAR_CLASSIFIERS
        case OP_CHARAP: /* char-alphabetic? */ s_retbool(Cisalpha(ivalue(car(sc->args))));
        case OP_CHARNP: /* char-numeric? */ s_retbool(Cisdigit(ivalue(car(sc->args))));
        case OP_CHARWP: /* char-whitespace? */ s_retbool(Cisspace(ivalue(car(sc->args))));
        case OP_CHARUP: /* char-upper-case? */ s_retbool(Cisupper(ivalue(car(sc->args))));
        case OP_CHARLP: /* char-lower-case? */ s_retbool(Cislower(ivalue(car(sc->args))));
#endif
        case OP_PORTP: /* port? */ s_retbool(is_port(car(sc->args)));
        case OP_INPORTP: /* input-port? */ s_retbool(is_inport(car(sc->args)));
        case OP_OUTPORTP: /* output-port? */ s_retbool(is_outport(car(sc->args)));
        case OP_PROCP: /* procedure? */
            /*--
             * continuation should be procedure by the example
             * (call-with-current-continuation procedure?) ==> #t
             * in R^3 report sec. 6.9
             */
            s_retbool(
                is_proc(car(sc->args)) || is_closure(car(sc->args)) || is_continuation(car(sc->args))
                || is_foreign(car(sc->args))
            );
        case OP_PAIRP: /* pair? */ s_retbool(is_pair(car(sc->args)));
        case OP_LISTP:
            { /* list? */
                pointer slow, fast;
                slow = fast = car(sc->args);
                while (1) {
                    if (!is_pair(fast))
                        s_retbool(fast == sc->NIL);
                    fast = cdr(fast);
                    if (!is_pair(fast))
                        s_retbool(fast == sc->NIL);
                    fast = cdr(fast);
                    slow = cdr(slow);
                    if (fast == slow) {
                        /* the fast pointer has looped back around and caught up
                           with the slow pointer, hence the structure is circular,
                           not of finite length, and therefore not a list */
                        s_retbool(0);
                    }
                }
            }
        case OP_ENVP: /* environment? */ s_retbool(is_environment(car(sc->args)));
        case OP_VECTORP: /* vector? */ s_retbool(is_vector(car(sc->args)));
        case OP_EQ: /* eq? */ s_retbool(car(sc->args) == cadr(sc->args));
        case OP_EQV: /* eqv? */ s_retbool(eqv(car(sc->args), cadr(sc->args)));
        default: sprintf(sc->strbuff, "%d: illegal operator", sc->op); Error_0(sc, sc->strbuff);
    }
    return sc->T;
}
 
static pointer
opexe_4(scheme* sc, enum scheme_opcodes op) {
    pointer x, y;
 
    switch (op) {
        case OP_FORCE: /* force */
            sc->code = car(sc->args);
            if (is_promise(sc->code)) {
                /* Should change type to closure here */
                s_save(sc, OP_SAVE_FORCED, sc->NIL, sc->code);
                sc->args = sc->NIL;
                s_goto(sc, OP_APPLY);
            } else {
                s_return(sc, sc->code);
            }
 
        case OP_SAVE_FORCED: /* Save forced value replacing promise */
            memcpy(sc->code, sc->value, sizeof(struct cell));
            s_return(sc, sc->value);
 
        case OP_WRITE:      /* write */
        case OP_DISPLAY:    /* display */
        case OP_WRITE_CHAR: /* write-char */
            if (is_pair(cdr(sc->args))) {
                if (cadr(sc->args) != sc->outport) {
                    x = cons(sc, sc->outport, sc->NIL);
                    s_save(sc, OP_SET_OUTPORT, x, sc->NIL);
                    sc->outport = cadr(sc->args);
                }
            }
            sc->args = car(sc->args);
            if (op == OP_WRITE) {
                sc->print_flag = 1;
            } else {
                sc->print_flag = 0;
            }
            s_goto(sc, OP_P0LIST);
 
        case OP_NEWLINE: /* newline */
            if (is_pair(sc->args)) {
                if (car(sc->args) != sc->outport) {
                    x = cons(sc, sc->outport, sc->NIL);
                    s_save(sc, OP_SET_OUTPORT, x, sc->NIL);
                    sc->outport = car(sc->args);
                }
            }
            putstr(sc, "\n");
            s_return(sc, sc->T);
 
        case OP_ERR0: /* error */
            sc->retcode = -1;
            if (!is_string(car(sc->args))) {
                sc->args = cons(sc, mk_string(sc, " -- "), sc->args);
                setimmutable(car(sc->args));
            }
            putstr(sc, "Error: ");
            putstr(sc, strvalue(car(sc->args)));
            sc->args = cdr(sc->args);
            s_goto(sc, OP_ERR1);
 
        case OP_ERR1: /* error */
            putstr(sc, " ");
            if (sc->args != sc->NIL) {
                s_save(sc, OP_ERR1, cdr(sc->args), sc->NIL);
                sc->args       = car(sc->args);
                sc->print_flag = 1;
                s_goto(sc, OP_P0LIST);
            } else {
                putstr(sc, "\n");
                if (sc->interactive_repl) {
                    s_goto(sc, OP_T0LVL);
                } else {
                    return sc->NIL;
                }
            }
 
        case OP_REVERSE: /* reverse */ s_return(sc, reverse(sc, car(sc->args)));
 
        case OP_LIST_STAR: /* list* */ s_return(sc, list_star(sc, sc->args));
 
        case OP_APPEND: /* append */
            if (sc->args == sc->NIL) {
                s_return(sc, sc->NIL);
            }
            x = car(sc->args);
            if (cdr(sc->args) == sc->NIL) {
                s_return(sc, sc->args);
            }
            for (y = cdr(sc->args); y != sc->NIL; y = cdr(y)) {
                x = append(sc, x, car(y));
            }
            s_return(sc, x);
 
#if USE_PLIST
        case OP_PUT: /* put */
            if (!hasprop(car(sc->args)) || !hasprop(cadr(sc->args))) {
                Error_0(sc, "illegal use of put");
            }
            for (x = symprop(car(sc->args)), y = cadr(sc->args); x != sc->NIL; x = cdr(x)) {
                if (caar(x) == y) {
                    break;
                }
            }
            if (x != sc->NIL)
                cdar(x) = caddr(sc->args);
            else
                symprop(car(sc->args)) = cons(sc, cons(sc, y, caddr(sc->args)), symprop(car(sc->args)));
            s_return(sc, sc->T);
 
        case OP_GET: /* get */
            if (!hasprop(car(sc->args)) || !hasprop(cadr(sc->args))) {
                Error_0(sc, "illegal use of get");
            }
            for (x = symprop(car(sc->args)), y = cadr(sc->args); x != sc->NIL; x = cdr(x)) {
                if (caar(x) == y) {
                    break;
                }
            }
            if (x != sc->NIL) {
                s_return(sc, cdar(x));
            } else {
                s_return(sc, sc->NIL);
            }
#endif                /* USE_PLIST */
        case OP_QUIT: /* quit */
            if (is_pair(sc->args)) {
                sc->retcode = ivalue(car(sc->args));
            }
            return (sc->NIL);
 
        case OP_GC: /* gc */ gc(sc, sc->NIL, sc->NIL); s_return(sc, sc->T);
 
        case OP_GCVERB: /* gc-verbose */
            {
                int was = sc->gc_verbose;
 
                sc->gc_verbose = (car(sc->args) != sc->F);
                s_retbool(was);
            }
 
        case OP_NEWSEGMENT: /* new-segment */
            if (!is_pair(sc->args) || !is_number(car(sc->args))) {
                Error_0(sc, "new-segment: argument must be a number");
            }
            alloc_cellseg(sc, (int)ivalue(car(sc->args)));
            s_return(sc, sc->T);
 
        case OP_OBLIST: /* oblist */ s_return(sc, oblist_all_symbols(sc));
 
        case OP_CURR_INPORT: /* current-input-port */ s_return(sc, sc->inport);
 
        case OP_CURR_OUTPORT: /* current-output-port */ s_return(sc, sc->outport);
 
        case OP_OPEN_INFILE:    /* open-input-file */
        case OP_OPEN_OUTFILE:   /* open-output-file */
        case OP_OPEN_INOUTFILE: /* open-input-output-file */
            {
                int     prop = 0;
                pointer p;
                switch (op) {
                    case OP_OPEN_INFILE: prop = port_input; break;
                    case OP_OPEN_OUTFILE: prop = port_output; break;
                    case OP_OPEN_INOUTFILE: prop = port_input | port_output; break;
                    default:;
                }
                p = port_from_filename(sc, strvalue(car(sc->args)), prop);
                if (p == sc->NIL) {
                    s_return(sc, sc->F);
                }
                s_return(sc, p);
            }
 
#if USE_STRING_PORTS
        case OP_OPEN_INSTRING:    /* open-input-string */
        case OP_OPEN_OUTSTRING:   /* open-output-string */
        case OP_OPEN_INOUTSTRING: /* open-input-output-string */
            {
                int     prop = 0;
                pointer p;
                switch (op) {
                    case OP_OPEN_INSTRING: prop = port_input; break;
                    case OP_OPEN_OUTSTRING: prop = port_output; break;
                    case OP_OPEN_INOUTSTRING: prop = port_input | port_output; break;
                    default:;
                }
                p = port_from_string(
                    sc, strvalue(car(sc->args)), strvalue(car(sc->args)) + strlength(car(sc->args)), prop
                );
                if (p == sc->NIL) {
                    s_return(sc, sc->F);
                }
                s_return(sc, p);
            }
#endif
 
        case OP_CLOSE_INPORT: /* close-input-port */ port_close(sc, car(sc->args), port_input); s_return(sc, sc->T);
 
        case OP_CLOSE_OUTPORT: /* close-output-port */ port_close(sc, car(sc->args), port_output); s_return(sc, sc->T);
 
        case OP_INT_ENV: /* interaction-environment */ s_return(sc, sc->global_env);
 
        case OP_CURR_ENV: /* current-environment */ s_return(sc, sc->envir);
        default:;
    }
    return sc->T;
}
 
static pointer
opexe_5(scheme* sc, enum scheme_opcodes op) {
    pointer x;
 
    if (sc->nesting != 0) {
        int n       = sc->nesting;
        sc->nesting = 0;
        sc->retcode = -1;
        Error_1(sc, "unmatched parentheses:", mk_integer(sc, n));
    }
 
    switch (op) {
        /* ========== reading part ========== */
        case OP_READ:
            if (!is_pair(sc->args)) {
                s_goto(sc, OP_READ_INTERNAL);
            }
            if (!is_inport(car(sc->args))) {
                Error_1(sc, "read: not an input port:", car(sc->args));
            }
            if (car(sc->args) == sc->inport) {
                s_goto(sc, OP_READ_INTERNAL);
            }
            x          = sc->inport;
            sc->inport = car(sc->args);
            x          = cons(sc, x, sc->NIL);
            s_save(sc, OP_SET_INPORT, x, sc->NIL);
            s_goto(sc, OP_READ_INTERNAL);
 
        case OP_READ_CHAR: /* read-char */
        case OP_PEEK_CHAR: /* peek-char */
            {
                int c;
                if (is_pair(sc->args)) {
                    if (car(sc->args) != sc->inport) {
                        x = sc->inport;
                        x = cons(sc, x, sc->NIL);
                        s_save(sc, OP_SET_INPORT, x, sc->NIL);
                        sc->inport = car(sc->args);
                    }
                }
                c = inchar(sc);
                if (c == EOF) {
                    s_return(sc, sc->EOF_OBJ);
                }
                if (sc->op == OP_PEEK_CHAR) {
                    backchar(sc, c);
                }
                s_return(sc, mk_character(sc, c));
            }
 
        case OP_CHAR_READY: /* char-ready? */
            {
                pointer p = sc->inport;
                int     res;
                if (is_pair(sc->args)) {
                    p = car(sc->args);
                }
                res = p->_object._port->kind & port_string;
                s_retbool(res);
            }
 
        case OP_SET_INPORT: /* set-input-port */ sc->inport = car(sc->args); s_return(sc, sc->value);
 
        case OP_SET_OUTPORT: /* set-output-port */ sc->outport = car(sc->args); s_return(sc, sc->value);
 
        case OP_RDSEXPR:
            switch (sc->tok) {
                case TOK_EOF:
                    if (sc->inport == sc->loadport) {
                        sc->args = sc->NIL;
                        s_goto(sc, OP_QUIT);
                    } else {
                        s_return(sc, sc->EOF_OBJ);
                    }
                case TOK_COMMENT:
                    {
                        int c;
                        while ((c = inchar(sc)) != '\n' && c != EOF)
                            ;
                        sc->tok = token(sc);
                        s_goto(sc, OP_RDSEXPR);
                    }
                case TOK_VEC:
                    s_save(sc, OP_RDVEC, sc->NIL, sc->NIL);
                    /* fall through */
                case TOK_LPAREN:
                    sc->tok = token(sc);
                    if (sc->tok == TOK_RPAREN) {
                        s_return(sc, sc->NIL);
                    } else if (sc->tok == TOK_DOT) {
                        Error_0(sc, "syntax error: illegal dot expression");
                    } else {
                        sc->nesting_stack[sc->file_i]++;
                        s_save(sc, OP_RDLIST, sc->NIL, sc->NIL);
                        s_goto(sc, OP_RDSEXPR);
                    }
                case TOK_QUOTE:
                    s_save(sc, OP_RDQUOTE, sc->NIL, sc->NIL);
                    sc->tok = token(sc);
                    s_goto(sc, OP_RDSEXPR);
                case TOK_BQUOTE:
                    sc->tok = token(sc);
                    if (sc->tok == TOK_VEC) {
                        s_save(sc, OP_RDQQUOTEVEC, sc->NIL, sc->NIL);
                        sc->tok = TOK_LPAREN;
                        s_goto(sc, OP_RDSEXPR);
                    } else {
                        s_save(sc, OP_RDQQUOTE, sc->NIL, sc->NIL);
                    }
                    s_goto(sc, OP_RDSEXPR);
                case TOK_COMMA:
                    s_save(sc, OP_RDUNQUOTE, sc->NIL, sc->NIL);
                    sc->tok = token(sc);
                    s_goto(sc, OP_RDSEXPR);
                case TOK_ATMARK:
                    s_save(sc, OP_RDUQTSP, sc->NIL, sc->NIL);
                    sc->tok = token(sc);
                    s_goto(sc, OP_RDSEXPR);
                case TOK_ATOM: s_return(sc, mk_atom(sc, readstr_upto(sc, "();\t\n\r ")));
                case TOK_DQUOTE:
                    x = readstrexp(sc);
                    if (x == sc->F) {
                        Error_0(sc, "Error reading string");
                    }
                    setimmutable(x);
                    s_return(sc, x);
                case TOK_SHARP:
                    {
                        pointer f = find_slot_in_env(sc, sc->envir, sc->SHARP_HOOK, 1);
                        if (f == sc->NIL) {
                            Error_0(sc, "undefined sharp expression");
                        } else {
                            sc->code = cons(sc, slot_value_in_env(f), sc->NIL);
                            s_goto(sc, OP_EVAL);
                        }
                    }
                case TOK_SHARP_CONST:
                    if ((x = mk_sharp_const(sc, readstr_upto(sc, "();\t\n\r "))) == sc->NIL) {
                        Error_0(sc, "undefined sharp expression");
                    } else {
                        s_return(sc, x);
                    }
                default: Error_0(sc, "syntax error: illegal token");
            }
            break;
 
        case OP_RDLIST:
            {
                sc->args = cons(sc, sc->value, sc->args);
                sc->tok  = token(sc);
                if (sc->tok == TOK_COMMENT) {
                    int c;
                    while ((c = inchar(sc)) != '\n' && c != EOF)
                        ;
                    sc->tok = token(sc);
                }
                if (sc->tok == TOK_RPAREN) {
                    int c = inchar(sc);
                    if (c != '\n')
                        backchar(sc, c);
                    sc->nesting_stack[sc->file_i]--;
                    s_return(sc, reverse_in_place(sc, sc->NIL, sc->args));
                } else if (sc->tok == TOK_DOT) {
                    s_save(sc, OP_RDDOT, sc->args, sc->NIL);
                    sc->tok = token(sc);
                    s_goto(sc, OP_RDSEXPR);
                } else {
                    s_save(sc, OP_RDLIST, sc->args, sc->NIL);
                    ;
                    s_goto(sc, OP_RDSEXPR);
                }
            }
 
        case OP_RDDOT:
            if (token(sc) != TOK_RPAREN) {
                Error_0(sc, "syntax error: illegal dot expression");
            } else {
                sc->nesting_stack[sc->file_i]--;
                s_return(sc, reverse_in_place(sc, sc->value, sc->args));
            }
 
        case OP_RDQUOTE: s_return(sc, cons(sc, sc->QUOTE, cons(sc, sc->value, sc->NIL)));
 
        case OP_RDQQUOTE: s_return(sc, cons(sc, sc->QQUOTE, cons(sc, sc->value, sc->NIL)));
 
        case OP_RDQQUOTEVEC:
            s_return(
                sc, cons(
                        sc, mk_symbol(sc, "apply"),
                        cons(
                            sc, mk_symbol(sc, "vector"),
                            cons(sc, cons(sc, sc->QQUOTE, cons(sc, sc->value, sc->NIL)), sc->NIL)
                        )
                    )
            );
 
        case OP_RDUNQUOTE: s_return(sc, cons(sc, sc->UNQUOTE, cons(sc, sc->value, sc->NIL)));
 
        case OP_RDUQTSP: s_return(sc, cons(sc, sc->UNQUOTESP, cons(sc, sc->value, sc->NIL)));
 
        case OP_RDVEC:
            /*sc->code=cons(sc,mk_proc(sc,OP_VECTOR),sc->value);
            s_goto(sc,OP_EVAL); Cannot be quoted*/
            /*x=cons(sc,mk_proc(sc,OP_VECTOR),sc->value);
          s_return(sc,x); Cannot be part of pairs*/
            /*sc->code=mk_proc(sc,OP_VECTOR);
            sc->args=sc->value;
            s_goto(sc,OP_APPLY);*/
            sc->args = sc->value;
            s_goto(sc, OP_VECTOR);
 
        /* ========== printing part ========== */
        case OP_P0LIST:
            if (is_vector(sc->args)) {
                putstr(sc, "#(");
                sc->args = cons(sc, sc->args, mk_integer(sc, 0));
                s_goto(sc, OP_PVECFROM);
            } else if (is_environment(sc->args)) {
                putstr(sc, "#<ENVIRONMENT>");
                s_return(sc, sc->T);
            } else if (!is_pair(sc->args)) {
                printatom(sc, sc->args, sc->print_flag);
                s_return(sc, sc->T);
            } else if (car(sc->args) == sc->QUOTE && ok_abbrev(cdr(sc->args))) {
                putstr(sc, "'");
                sc->args = cadr(sc->args);
                s_goto(sc, OP_P0LIST);
            } else if (car(sc->args) == sc->QQUOTE && ok_abbrev(cdr(sc->args))) {
                putstr(sc, "`");
                sc->args = cadr(sc->args);
                s_goto(sc, OP_P0LIST);
            } else if (car(sc->args) == sc->UNQUOTE && ok_abbrev(cdr(sc->args))) {
                putstr(sc, ",");
                sc->args = cadr(sc->args);
                s_goto(sc, OP_P0LIST);
            } else if (car(sc->args) == sc->UNQUOTESP && ok_abbrev(cdr(sc->args))) {
                putstr(sc, ",@");
                sc->args = cadr(sc->args);
                s_goto(sc, OP_P0LIST);
            } else {
                putstr(sc, "(");
                s_save(sc, OP_P1LIST, cdr(sc->args), sc->NIL);
                sc->args = car(sc->args);
                s_goto(sc, OP_P0LIST);
            }
 
        case OP_P1LIST:
            if (is_pair(sc->args)) {
                s_save(sc, OP_P1LIST, cdr(sc->args), sc->NIL);
                putstr(sc, " ");
                sc->args = car(sc->args);
                s_goto(sc, OP_P0LIST);
            } else if (is_vector(sc->args)) {
                s_save(sc, OP_P1LIST, sc->NIL, sc->NIL);
                putstr(sc, " . ");
                s_goto(sc, OP_P0LIST);
            } else {
                if (sc->args != sc->NIL) {
                    putstr(sc, " . ");
                    printatom(sc, sc->args, sc->print_flag);
                }
                putstr(sc, ")");
                s_return(sc, sc->T);
            }
        case OP_PVECFROM:
            {
                int     i   = ivalue_unchecked(cdr(sc->args));
                pointer vec = car(sc->args);
                int     len = ivalue_unchecked(vec);
                if (i == len) {
                    putstr(sc, ")");
                    s_return(sc, sc->T);
                } else {
                    pointer elem                    = vector_elem(vec, i);
                    ivalue_unchecked(cdr(sc->args)) = i + 1;
                    s_save(sc, OP_PVECFROM, sc->args, sc->NIL);
                    sc->args = elem;
                    putstr(sc, " ");
                    s_goto(sc, OP_P0LIST);
                }
            }
 
        default: sprintf(sc->strbuff, "%d: illegal operator", sc->op); Error_0(sc, sc->strbuff);
    }
    return sc->T;
}
 
static pointer
opexe_6(scheme* sc, enum scheme_opcodes op) {
    pointer x, y;
    long    v;
 
    switch (op) {
        case OP_LIST_LENGTH: /* length */ /* a.k */
            v = list_length(sc, car(sc->args));
            if (v < 0) {
                Error_1(sc, "length: not a list:", car(sc->args));
            }
            s_return(sc, mk_integer(sc, v));
 
        case OP_ASSQ: /* assq */ /* a.k */
            x = car(sc->args);
            for (y = cadr(sc->args); is_pair(y); y = cdr(y)) {
                if (!is_pair(car(y))) {
                    Error_0(sc, "unable to handle non pair element");
                }
                if (x == caar(y))
                    break;
            }
            if (is_pair(y)) {
                s_return(sc, car(y));
            } else {
                s_return(sc, sc->F);
            }
 
        case OP_GET_CLOSURE: /* get-closure-code */ /* a.k */
            sc->args = car(sc->args);
            if (sc->args == sc->NIL) {
                s_return(sc, sc->F);
            } else if (is_closure(sc->args)) {
                s_return(sc, cons(sc, sc->LAMBDA, closure_code(sc->value)));
            } else if (is_macro(sc->args)) {
                s_return(sc, cons(sc, sc->LAMBDA, closure_code(sc->value)));
            } else {
                s_return(sc, sc->F);
            }
        case OP_CLOSUREP: /* closure? */
            /*
             * Note, macro object is also a closure.
             * Therefore, (closure? <#MACRO>) ==> #t
             */
            s_retbool(is_closure(car(sc->args)));
        case OP_MACROP: /* macro? */ s_retbool(is_macro(car(sc->args)));
        default: sprintf(sc->strbuff, "%d: illegal operator", sc->op); Error_0(sc, sc->strbuff);
    }
    return sc->T; /* NOTREACHED */
}
 
typedef pointer (*dispatch_func)(scheme*, enum scheme_opcodes);
 
typedef int (*test_predicate)(pointer);
 
static int
is_any(pointer p) {
    return 1;
}
 
static int
is_num_integer(pointer p) {
    return is_number(p) && ((p)->_object._number.is_fixnum);
}
 
static int
is_nonneg(pointer p) {
    return is_num_integer(p) && ivalue(p) >= 0;
}
 
/* Correspond carefully with following defines! */
static struct {
    test_predicate fct;
    const char*    kind;
} tests[] = {
    {             0,                      0}, /* unused */
    {        is_any,                      0},
    {     is_string,               "string"},
    {     is_symbol,               "symbol"},
    {       is_port,                 "port"},
    {             0,           "input port"},
    {             0,          "output_port"},
    {is_environment,          "environment"},
    {       is_pair,                 "pair"},
    {             0,          "pair or '()"},
    {  is_character,            "character"},
    {     is_vector,               "vector"},
    {     is_number,               "number"},
    {is_num_integer,              "integer"},
    {     is_nonneg, "non-negative integer"}
};
 
#define TST_NONE        0
#define TST_ANY         "\001"
#define TST_STRING      "\002"
#define TST_SYMBOL      "\003"
#define TST_PORT        "\004"
#define TST_INPORT      "\005"
#define TST_OUTPORT     "\006"
#define TST_ENVIRONMENT "\007"
#define TST_PAIR        "\010"
#define TST_LIST        "\011"
#define TST_CHAR        "\012"
#define TST_VECTOR      "\013"
#define TST_NUMBER      "\014"
#define TST_INTEGER     "\015"
#define TST_NATURAL     "\016"
 
typedef struct {
    dispatch_func func;
    char*         name;
    int           min_arity;
    int           max_arity;
    char*         arg_tests_encoding;
} op_code_info;
 
#define INF_ARG 0xffff
 
static op_code_info dispatch_table[] = {
#define _OP_DEF(A, B, C, D, E, OP) { A, B, C, D, E },
#include "opdefines.h"
    { 0 }
};
 
static const char*
procname(pointer x) {
    int         n    = procnum(x);
    const char* name = dispatch_table[n].name;
    if (name == 0) {
        name = "ILLEGAL!";
    }
    return name;
}
 
/* kernel of this interpreter */
static void
Eval_Cycle(scheme* sc, enum scheme_opcodes op) {
    int count = 0;
    /*int old_op;*/
 
    sc->op = op;
    for (;;) {
        op_code_info* pcd = dispatch_table + sc->op;
        if (pcd->name != 0) { /* if built-in function, check arguments */
            char msg[512];
            int  ok = 1;
            int  n  = list_length(sc, sc->args);
 
            /* Check number of arguments */
            if (n < pcd->min_arity) {
                ok = 0;
                sprintf(
                    msg, "%s: needs%s %d argument(s)", pcd->name, pcd->min_arity == pcd->max_arity ? "" : " at least",
                    pcd->min_arity
                );
            }
            if (ok && n > pcd->max_arity) {
                ok = 0;
                sprintf(
                    msg, "%s: needs%s %d argument(s)", pcd->name, pcd->min_arity == pcd->max_arity ? "" : " at most",
                    pcd->max_arity
                );
            }
            if (ok) {
                if (pcd->arg_tests_encoding != 0) {
                    int         i = 0;
                    int         j;
                    const char* t       = pcd->arg_tests_encoding;
                    pointer     arglist = sc->args;
                    do {
                        pointer arg = car(arglist);
                        j           = (int)t[0];
                        if (j == TST_INPORT[0]) {
                            if (!is_inport(arg))
                                break;
                        } else if (j == TST_OUTPORT[0]) {
                            if (!is_outport(arg))
                                break;
                        } else if (j == TST_LIST[0]) {
                            if (arg != sc->NIL && !is_pair(arg))
                                break;
                        } else {
                            if (!tests[j].fct(arg))
                                break;
                        }
 
                        if (t[1] != 0) { /* last test is replicated as necessary */
                            t++;
                        }
                        arglist = cdr(arglist);
                        i++;
                    } while (i < n);
                    if (i < n) {
                        ok = 0;
                        sprintf(msg, "%s: argument %d must be: %s", pcd->name, i + 1, tests[j].kind);
                    }
                }
            }
            if (!ok) {
                if (_Error_1(sc, msg, 0) == sc->NIL) {
                    return;
                }
                pcd = dispatch_table + sc->op;
            }
        }
        /*old_op=sc->op;*/
        if (pcd->func(sc, (enum scheme_opcodes)sc->op) == sc->NIL) {
            return;
        }
        if (sc->no_memory) {
            fprintf(stderr, "No memory!\n");
            return;
        }
        count++;
    }
}
 
/* ========== Initialization of internal keywords ========== */
 
static void
assign_syntax(scheme* sc, char* name) {
    pointer x;
 
    x = oblist_add_by_name(sc, name);
    typeflag(x) |= T_SYNTAX;
}
 
static void
assign_proc(scheme* sc, enum scheme_opcodes op, char* name) {
    pointer x, y;
 
    x = mk_symbol(sc, name);
    y = mk_proc(sc, op);
    new_slot_in_env(sc, x, y);
}
 
static pointer
mk_proc(scheme* sc, enum scheme_opcodes op) {
    pointer y;
 
    y                   = get_cell(sc, sc->NIL, sc->NIL);
    typeflag(y)         = (T_PROC | T_ATOM);
    ivalue_unchecked(y) = (long)op;
    set_integer(y);
    return y;
}
 
/* Hard-coded for the given keywords. Remember to rewrite if more are added! */
static int
syntaxnum(pointer p) {
    const char* s = strvalue(car(p));
    switch (strlength(car(p))) {
        case 2:
            if (s[0] == 'i')
                return OP_IF0; /* if */
            else
                return OP_OR0; /* or */
        case 3:
            if (s[0] == 'a')
                return OP_AND0; /* and */
            else
                return OP_LET0; /* let */
        case 4:
            switch (s[3]) {
                case 'e': return OP_CASE0;   /* case */
                case 'd': return OP_COND0;   /* cond */
                case '*': return OP_LET0AST; /* let* */
                default: return OP_SET0;     /* set! */
            }
        case 5:
            switch (s[2]) {
                case 'g': return OP_BEGIN;  /* begin */
                case 'l': return OP_DELAY;  /* delay */
                case 'c': return OP_MACRO0; /* macro */
                default: return OP_QUOTE;   /* quote */
            }
        case 6:
            switch (s[2]) {
                case 'm': return OP_LAMBDA; /* lambda */
                case 'f': return OP_DEF0;   /* define */
                default: return OP_LET0REC; /* letrec */
            }
        default: return OP_C0STREAM; /* cons-stream */
    }
}
 
/* initialization of TinyScheme */
#if USE_INTERFACE
INTERFACE static pointer
s_cons(scheme* sc, pointer a, pointer b) {
    return cons(sc, a, b);
}
 
INTERFACE static pointer
s_immutable_cons(scheme* sc, pointer a, pointer b) {
    return immutable_cons(sc, a, b);
}
 
static struct scheme_interface vtbl = { scheme_define,
                                        s_cons,
                                        s_immutable_cons,
                                        mk_integer,
                                        mk_real,
                                        mk_symbol,
                                        gensym,
                                        mk_string,
                                        mk_counted_string,
                                        mk_character,
                                        mk_vector,
                                        mk_foreign_func,
                                        putstr,
                                        putcharacter,
 
                                        is_string,
                                        string_value,
                                        is_number,
                                        nvalue,
                                        ivalue,
                                        rvalue,
                                        is_integer,
                                        is_real,
                                        is_character,
                                        charvalue,
                                        is_vector,
                                        ivalue,
                                        fill_vector,
                                        vector_elem,
                                        set_vector_elem,
                                        is_port,
                                        is_pair,
                                        pair_car,
                                        pair_cdr,
                                        set_car,
                                        set_cdr,
 
                                        is_symbol,
                                        symname,
 
                                        is_syntax,
                                        is_proc,
                                        is_foreign,
                                        syntaxname,
                                        is_closure,
                                        is_macro,
                                        closure_code,
                                        closure_env,
 
                                        is_continuation,
                                        is_promise,
                                        is_environment,
                                        is_immutable,
                                        setimmutable,
 
                                        scheme_load_file,
                                        scheme_load_string };
#endif
 
scheme*
scheme_init_new() {
    scheme* sc = (scheme*)malloc(sizeof(scheme));
    if (!scheme_init(sc)) {
        free(sc);
        return 0;
    } else {
        return sc;
    }
}
 
scheme*
scheme_init_new_custom_alloc(func_alloc malloc, func_dealloc free) {
    scheme* sc = (scheme*)malloc(sizeof(scheme));
    if (!scheme_init_custom_alloc(sc, malloc, free)) {
        free(sc);
        return 0;
    } else {
        return sc;
    }
}
 
int
scheme_init(scheme* sc) {
    return scheme_init_custom_alloc(sc, malloc, free);
}
 
int
scheme_init_custom_alloc(scheme* sc, func_alloc malloc, func_dealloc free) {
    int     i, n = sizeof(dispatch_table) / sizeof(dispatch_table[0]);
    pointer x;
 
    num_zero.is_fixnum    = 1;
    num_zero.value.ivalue = 0;
    num_one.is_fixnum     = 1;
    num_one.value.ivalue  = 1;
 
#if USE_INTERFACE
    sc->vptr = &vtbl;
#endif
    sc->gensym_cnt       = 0;
    sc->malloc           = malloc;
    sc->free             = free;
    sc->last_cell_seg    = -1;
    sc->sink             = &sc->_sink;
    sc->NIL              = &sc->_NIL;
    sc->T                = &sc->_HASHT;
    sc->F                = &sc->_HASHF;
    sc->EOF_OBJ          = &sc->_EOF_OBJ;
    sc->free_cell        = &sc->_NIL;
    sc->fcells           = 0;
    sc->no_memory        = 0;
    sc->inport           = sc->NIL;
    sc->outport          = sc->NIL;
    sc->save_inport      = sc->NIL;
    sc->loadport         = sc->NIL;
    sc->nesting          = 0;
    sc->interactive_repl = 0;
 
    if (alloc_cellseg(sc, FIRST_CELLSEGS) != FIRST_CELLSEGS) {
        sc->no_memory = 1;
        return 0;
    }
    sc->gc_verbose = 0;
    dump_stack_initialize(sc);
    sc->code    = sc->NIL;
    sc->tracing = 0;
 
    /* init sc->NIL */
    typeflag(sc->NIL) = (T_ATOM | MARK);
    car(sc->NIL) = cdr(sc->NIL) = sc->NIL;
    /* init T */
    typeflag(sc->T) = (T_ATOM | MARK);
    car(sc->T) = cdr(sc->T) = sc->T;
    /* init F */
    typeflag(sc->F) = (T_ATOM | MARK);
    car(sc->F) = cdr(sc->F) = sc->F;
    sc->oblist              = oblist_initial_value(sc);
    /* init global_env */
    new_frame_in_env(sc, sc->NIL);
    sc->global_env = sc->envir;
    /* init else */
    x = mk_symbol(sc, "else");
    new_slot_in_env(sc, x, sc->T);
 
    assign_syntax(sc, "lambda");
    assign_syntax(sc, "quote");
    assign_syntax(sc, "define");
    assign_syntax(sc, "if");
    assign_syntax(sc, "begin");
    assign_syntax(sc, "set!");
    assign_syntax(sc, "let");
    assign_syntax(sc, "let*");
    assign_syntax(sc, "letrec");
    assign_syntax(sc, "cond");
    assign_syntax(sc, "delay");
    assign_syntax(sc, "and");
    assign_syntax(sc, "or");
    assign_syntax(sc, "cons-stream");
    assign_syntax(sc, "macro");
    assign_syntax(sc, "case");
 
    for (i = 0; i < n; i++) {
        if (dispatch_table[i].name != 0) {
            assign_proc(sc, (enum scheme_opcodes)i, dispatch_table[i].name);
        }
    }
 
    /* initialization of global pointers to special symbols */
    sc->LAMBDA     = mk_symbol(sc, "lambda");
    sc->QUOTE      = mk_symbol(sc, "quote");
    sc->QQUOTE     = mk_symbol(sc, "quasiquote");
    sc->UNQUOTE    = mk_symbol(sc, "unquote");
    sc->UNQUOTESP  = mk_symbol(sc, "unquote-splicing");
    sc->FEED_TO    = mk_symbol(sc, "=>");
    sc->COLON_HOOK = mk_symbol(sc, "*colon-hook*");
    sc->ERROR_HOOK = mk_symbol(sc, "*error-hook*");
    sc->SHARP_HOOK = mk_symbol(sc, "*sharp-hook*");
 
    return !sc->no_memory;
}
 
void
scheme_set_input_port_file(scheme* sc, FILE* fin) {
    sc->inport = port_from_file(sc, fin, port_input);
}
 
void
scheme_set_input_port_string(scheme* sc, char* start, char* past_the_end) {
    sc->inport = port_from_string(sc, start, past_the_end, port_input);
}
 
void
scheme_set_output_port_file(scheme* sc, FILE* fout) {
    sc->outport = port_from_file(sc, fout, port_output);
}
 
void
scheme_set_output_port_string(scheme* sc, char* start, char* past_the_end) {
    sc->outport = port_from_string(sc, start, past_the_end, port_output);
}
 
void
scheme_set_external_data(scheme* sc, void* p) {
    sc->ext_data = p;
}
 
void
scheme_deinit(scheme* sc) {
    int i;
 
    sc->oblist     = sc->NIL;
    sc->global_env = sc->NIL;
    dump_stack_free(sc);
    sc->envir = sc->NIL;
    sc->code  = sc->NIL;
    sc->args  = sc->NIL;
    sc->value = sc->NIL;
    if (is_port(sc->inport)) {
        typeflag(sc->inport) = T_ATOM;
    }
    sc->inport  = sc->NIL;
    sc->outport = sc->NIL;
    if (is_port(sc->save_inport)) {
        typeflag(sc->save_inport) = T_ATOM;
    }
    sc->save_inport = sc->NIL;
    if (is_port(sc->loadport)) {
        typeflag(sc->loadport) = T_ATOM;
    }
    sc->loadport   = sc->NIL;
    sc->gc_verbose = 0;
    gc(sc, sc->NIL, sc->NIL);
 
    for (i = 0; i <= sc->last_cell_seg; i++) {
        sc->free(sc->alloc_seg[i]);
    }
}
 
void
scheme_load_file(scheme* sc, FILE* fin) {
    dump_stack_reset(sc);
    sc->envir                        = sc->global_env;
    sc->file_i                       = 0;
    sc->load_stack[0].kind           = port_input | port_file;
    sc->load_stack[0].rep.stdio.file = fin;
    sc->loadport                     = mk_port(sc, sc->load_stack);
    sc->retcode                      = 0;
    if (fin == stdin) {
        sc->interactive_repl = 1;
    }
    sc->inport = sc->loadport;
    Eval_Cycle(sc, OP_T0LVL);
    typeflag(sc->loadport) = T_ATOM;
    if (sc->retcode == 0) {
        sc->retcode = sc->nesting != 0;
    }
}
 
void
scheme_load_string(scheme* sc, const char* cmd) {
    dump_stack_reset(sc);
    sc->envir                                 = sc->global_env;
    sc->file_i                                = 0;
    sc->load_stack[0].kind                    = port_input | port_string;
    sc->load_stack[0].rep.string.start        = (char*)cmd; /* This func respects const */
    sc->load_stack[0].rep.string.past_the_end = (char*)cmd + strlen(cmd);
    sc->load_stack[0].rep.string.curr         = (char*)cmd;
    sc->loadport                              = mk_port(sc, sc->load_stack);
    sc->retcode                               = 0;
    sc->interactive_repl                      = 0;
    sc->inport                                = sc->loadport;
    Eval_Cycle(sc, OP_T0LVL);
    typeflag(sc->loadport) = T_ATOM;
    if (sc->retcode == 0) {
        sc->retcode = sc->nesting != 0;
    }
}
 
void
scheme_define(scheme* sc, pointer envir, pointer symbol, pointer value) {
    pointer x;
 
    x = find_slot_in_env(sc, envir, symbol, 0);
    if (x != sc->NIL) {
        set_slot_in_env(sc, x, value);
    } else {
        new_slot_spec_in_env(sc, envir, symbol, value);
    }
}
 
#if !STANDALONE
void
scheme_apply0(scheme* sc, const char* procname) {
    pointer carx = mk_symbol(sc, procname);
    pointer cdrx = sc->NIL;
 
    dump_stack_reset(sc);
    sc->envir            = sc->global_env;
    sc->code             = cons(sc, carx, cdrx);
    sc->interactive_repl = 0;
    sc->retcode          = 0;
    Eval_Cycle(sc, OP_EVAL);
}
 
void
scheme_call(scheme* sc, pointer func, pointer args) {
    dump_stack_reset(sc);
    sc->envir            = sc->global_env;
    sc->args             = args;
    sc->code             = func;
    sc->interactive_repl = 0;
    sc->retcode          = 0;
    Eval_Cycle(sc, OP_APPLY);
}
#endif
 
/* ========== Main ========== */
 
#if STANDALONE
 
#ifdef macintosh
int
main() {
    extern MacTS_main(int argc, char** argv);
    char** argv;
    int    argc = ccommand(&argv);
    MacTS_main(argc, argv);
    return 0;
}
int
MacTS_main(int argc, char** argv) {
#else
int
main(int argc, char** argv) {
#endif
    scheme sc;
    FILE*  fin       = 0;
    char*  file_name = InitFile;
    int    retcode;
    int    isfile = 1;
 
    if (argc == 1) {
        printf(banner);
    }
    if (argc == 2 && strcmp(argv[1], "-?") == 0) {
        printf(
            "Usage: %s [-? | <file1> <file2> ... | -1 <file> <arg1> <arg2> ...]\n\tUse - as filename for stdin.\n",
            argv[0]
        );
        return 1;
    }
    if (!scheme_init(&sc)) {
        fprintf(stderr, "Could not initialize!\n");
        return 2;
    }
    scheme_set_input_port_file(&sc, stdin);
    scheme_set_output_port_file(&sc, stdout);
#if USE_DL
    scheme_define(&sc, sc.global_env, mk_symbol(&sc, "load-extension"), mk_foreign_func(&sc, scm_load_ext));
#endif
    argv++;
    if (access(file_name, 0) != 0) {
        char* p = getenv("TINYSCHEMEINIT");
        if (p != 0) {
            file_name = p;
        }
    }
    do {
        if (strcmp(file_name, "-") == 0) {
            fin = stdin;
        } else if (strcmp(file_name, "-1") == 0 || strcmp(file_name, "-c") == 0) {
            pointer args = sc.NIL;
            isfile       = file_name[1] == '1';
            file_name    = *argv++;
            if (strcmp(file_name, "-") == 0) {
                fin = stdin;
            } else if (isfile) {
                fin = fopen(file_name, "r");
            }
            for (; *argv; argv++) {
                pointer value = mk_string(&sc, *argv);
                args          = cons(&sc, value, args);
            }
            args = reverse_in_place(&sc, sc.NIL, args);
            scheme_define(&sc, sc.global_env, mk_symbol(&sc, "*args*"), args);
 
        } else {
            fin = fopen(file_name, "r");
        }
        if (isfile && fin == 0) {
            fprintf(stderr, "Could not open file %s\n", file_name);
        } else {
            if (isfile) {
                scheme_load_file(&sc, fin);
            } else {
                scheme_load_string(&sc, file_name);
            }
            if (!isfile || fin != stdin) {
                if (sc.retcode != 0) {
                    fprintf(stderr, "Errors encountered reading %s\n", file_name);
                }
                if (isfile) {
                    fclose(fin);
                }
            }
        }
        file_name = *argv++;
    } while (file_name != 0);
    if (argc == 1) {
        scheme_load_file(&sc, stdin);
    }
    retcode = sc.retcode;
    scheme_deinit(&sc);
 
    return retcode;
}
 
#endif