cvs/stack/stack.c

/* -*- coding: utf-8; -*- */
/*
    stack - an interactive interpreter for a stack-based language
    Copyright (C) 2002  Mats Alritzson and Teddy Hogeborn

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

    Authors: Mats Alritzson <masse@fukt.bth.se>
             Teddy Hogeborn <teddy@fukt.bth.se>
*/

#define CAR(X) ((X)->content.c->car)
#define CDR(X) ((X)->content.c->cdr)

/* printf, sscanf, fgets, fprintf, fopen, perror */
#include <stdio.h>
/* exit, EXIT_SUCCESS, malloc, free */
#include <stdlib.h>
/* NULL */
#include <stddef.h>
/* dlopen, dlsym, dlerror */
#include <dlfcn.h>
/* strcmp, strcpy, strlen, strcat, strdup */
#include <string.h>
/* getopt, STDIN_FILENO, STDOUT_FILENO, usleep */
#include <unistd.h>
/* EX_NOINPUT, EX_USAGE */
#include <sysexits.h>
/* assert */
#include <assert.h>

#ifdef __linux__
/* mtrace, muntrace */
#include <mcheck.h>
/* ioctl */
#include <sys/ioctl.h>
/* KDMKTONE */
#include <linux/kd.h>
#endif /* __linux__ */

#include "stack.h"

/* Initialize a newly created environment */
void init_env(environment *env)
{
  int i;

  env->gc_limit= 400000;
  env->gc_count= 0;
  env->gc_ref= NULL;

  env->head= new_val(env);
  for(i= 0; i<HASHTBLSIZE; i++)
    env->symbols[i]= NULL;
  env->err= 0;
  env->in_string= NULL;
  env->free_string= NULL;
  env->inputstream= stdin;
  env->interactive= 1;
}

void printerr(const char* in_string)
{
  fprintf(stderr, "Err: %s\n", in_string);
}

/* Discard the top element of the stack. */
extern void toss(environment *env)
{
  if(env->head->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }
  
  env->head= CDR(env->head); /* Remove the top stack item */
}

/* Returns a pointer to a pointer to an element in the hash table. */
symbol **hash(hashtbl in_hashtbl, const char *in_string)
{
  int i= 0;
  unsigned int out_hash= 0;
  char key= '\0';
  symbol **position;
  
  while(1){                     /* Hash in_string */
    key= in_string[i++];
    if(key=='\0')
      break;
    out_hash= out_hash*32+key;
  }

  out_hash= out_hash%HASHTBLSIZE;
  position= &(in_hashtbl[out_hash]);

  while(1){
    if(*position==NULL)         /* If empty */
      return position;
    
    if(strcmp(in_string, (*position)->id)==0) /* If match */
      return position;

    position= &((*position)->next); /* Try next */
  }
}

/* Create new value */
value* new_val(environment *env)
{
  value *nval= malloc(sizeof(value));
  stackitem *nitem= malloc(sizeof(stackitem));

  assert(nval != NULL);
  assert(nitem != NULL);

  nval->content.ptr= NULL;
  nval->type= empty;

  nitem->item= nval;
  nitem->next= env->gc_ref;

  env->gc_ref= nitem;

  env->gc_count += sizeof(value);
  nval->gc.flag.mark= 0;
  nval->gc.flag.protect= 0;

  return nval;
}

/* Mark values recursively. 
   Marked values are not collected by the GC. */
inline void gc_mark(value *val)
{
  if(val==NULL || val->gc.flag.mark)
    return;

  val->gc.flag.mark= 1;

  if(val->type==tcons) {
    gc_mark(CAR(val));
    gc_mark(CDR(val));
  }
}

inline void gc_maybe(environment *env)
{
  if(env->gc_count < env->gc_limit)
    return;
  else
    return gc_init(env);
}

/* Start GC */
extern void gc_init(environment *env)
{
  stackitem *new_head= NULL, *titem;
  symbol *tsymb;
  int i;

  if(env->interactive)
    printf("Garbage collecting.");

  /* Mark values on stack */
  gc_mark(env->head);

  if(env->interactive)
    printf(".");


  /* Mark values in hashtable */
  for(i= 0; i<HASHTBLSIZE; i++)
    for(tsymb= env->symbols[i]; tsymb!=NULL; tsymb= tsymb->next)
      if (tsymb->val != NULL)
        gc_mark(tsymb->val);


  if(env->interactive)
    printf(".");

  env->gc_count= 0;

  while(env->gc_ref!=NULL) {    /* Sweep unused values */

    if(!(env->gc_ref->item->gc.no_gc)){ /* neither mark nor protect */

      /* Remove content */
      switch(env->gc_ref->item->type){
      case string:
        free(env->gc_ref->item->content.ptr);
        break;
      case tcons:
        free(env->gc_ref->item->content.c);
        break;
      case empty:
      case integer:
      case tfloat:
      case func:
      case symb:
        /* Symbol strings are freed when walking the hash table */
      }

      free(env->gc_ref->item);  /* Remove from gc_ref */
      titem= env->gc_ref->next;
      free(env->gc_ref);        /* Remove value */
      env->gc_ref= titem;
      continue;
    }
#ifdef DEBUG
    printf("Kept value (%p)", env->gc_ref->item);
    if(env->gc_ref->item->gc.flag.mark)
      printf(" (marked)");
    if(env->gc_ref->item->gc.flag.protect)
      printf(" (protected)");
    switch(env->gc_ref->item->type){
    case integer:
      printf(" integer: %d", env->gc_ref->item->content.i);
      break;
    case func:
      printf(" func: %p", env->gc_ref->item->content.ptr);
      break;
    case symb:
      printf(" symb: %s", env->gc_ref->item->content.sym->id);
      break;
    case tcons:
      printf(" tcons: %p\t%p", env->gc_ref->item->content.c->car,
             env->gc_ref->item->content.c->cdr);
      break;
    default:
      printf(" <unknown %d>", (env->gc_ref->item->type));
    }
    printf("\n");
#endif /* DEBUG */

    /* Keep values */     
    env->gc_count += sizeof(value);
    if(env->gc_ref->item->type==string)
      env->gc_count += strlen(env->gc_ref->item->content.ptr)+1;
    
    titem= env->gc_ref->next;
    env->gc_ref->next= new_head;
    new_head= env->gc_ref;
    new_head->item->gc.flag.mark= 0;
    env->gc_ref= titem;
  }

  if (env->gc_limit < env->gc_count*2)
    env->gc_limit= env->gc_count*2;

  env->gc_ref= new_head;

  if(env->interactive)
    printf("done (%d bytes still allocated)\n", env->gc_count);

}

/* Protect values from GC */
void protect(value *val)
{
  if(val==NULL || val->gc.flag.protect)
    return;

  val->gc.flag.protect= 1;

  if(val->type==tcons) {
    protect(CAR(val));
    protect(CDR(val));
  }
}

/* Unprotect values from GC */
void unprotect(value *val)
{
  if(val==NULL || !(val->gc.flag.protect))
    return;

  val->gc.flag.protect= 0;

  if(val->type==tcons) {
    unprotect(CAR(val));
    unprotect(CDR(val));
  }
}

/* Push a value onto the stack */
void push_val(environment *env, value *val)
{
  value *new_value= new_val(env);

  new_value->content.c= malloc(sizeof(pair));
  assert(new_value->content.c!=NULL);
  env->gc_count += sizeof(pair);
  new_value->type= tcons;
  CAR(new_value)= val;
  CDR(new_value)= env->head;
  env->head= new_value;
}

/* Push an integer onto the stack */
void push_int(environment *env, int in_val) 
{
  value *new_value= new_val(env);
  
  new_value->content.i= in_val;
  new_value->type= integer;

  push_val(env, new_value);
}

/* Push a floating point number onto the stack */
void push_float(environment *env, float in_val)
{
  value *new_value= new_val(env);

  new_value->content.f= in_val;
  new_value->type= tfloat;

  push_val(env, new_value);
}

/* Copy a string onto the stack. */
void push_cstring(environment *env, const char *in_string)
{
  value *new_value= new_val(env);
  int length= strlen(in_string)+1;

  new_value->content.ptr= malloc(length);
  assert(new_value != NULL);
  env->gc_count += length;
  strcpy(new_value->content.ptr, in_string);
  new_value->type= string;

  push_val(env, new_value);
}

/* Mangle a symbol name to a valid C identifier name */
char *mangle_str(const char *old_string)
{
  char validchars[]= "0123456789abcdef";
  char *new_string, *current;

  new_string= malloc((strlen(old_string)*2)+4);
  assert(new_string != NULL);
  strcpy(new_string, "sx_");    /* Stack eXternal */
  current= new_string+3;
  while(old_string[0] != '\0'){
    current[0]= validchars[(unsigned char)(old_string[0])/16];
    current[1]= validchars[(unsigned char)(old_string[0])%16];
    current+= 2;
    old_string++;
  }
  current[0]= '\0';

  return new_string;            /* The caller must free() it */
}

extern void mangle(environment *env)
{
  char *new_string;

  if(env->head->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CAR(env->head)->type!=string) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }

  new_string= 
    mangle_str((const char *)(CAR(env->head)->content.ptr));

  toss(env);
  if(env->err) return;

  push_cstring(env, new_string);
}

/* Push a symbol onto the stack. */
void push_sym(environment *env, const char *in_string)
{
  value *new_value;             /* A new symbol value */
  /* ...which might point to... */
  symbol **new_symbol;          /* (if needed) A new actual symbol */
  /* ...which, if possible, will be bound to... */
  value *new_fvalue;            /* (if needed) A new function value */
  /* ...which will point to... */
  void *funcptr;                /* A function pointer */

  static void *handle= NULL;    /* Dynamic linker handle */
  const char *dlerr;            /* Dynamic linker error */
  char *mangled;                /* Mangled function name */

  new_value= new_val(env);
  protect(new_value);
  new_fvalue= new_val(env);
  protect(new_fvalue);

  /* The new value is a symbol */
  new_value->type= symb;

  /* Look up the symbol name in the hash table */
  new_symbol= hash(env->symbols, in_string);
  new_value->content.ptr= *new_symbol;

  if(*new_symbol==NULL) { /* If symbol was undefined */

    /* Create a new symbol */
    (*new_symbol)= malloc(sizeof(symbol));
    assert((*new_symbol) != NULL);
    (*new_symbol)->val= NULL;   /* undefined value */
    (*new_symbol)->next= NULL;
    (*new_symbol)->id= malloc(strlen(in_string)+1);
    assert((*new_symbol)->id != NULL);
    strcpy((*new_symbol)->id, in_string);

    /* Intern the new symbol in the hash table */
    new_value->content.ptr= *new_symbol;

    /* Try to load the symbol name as an external function, to see if
       we should bind the symbol to a new function pointer value */
    if(handle==NULL)            /* If no handle */
      handle= dlopen(NULL, RTLD_LAZY);

    mangled= mangle_str(in_string); /* mangle the name */
    funcptr= dlsym(handle, mangled); /* and try to find it */

    dlerr= dlerror();
    if(dlerr != NULL) {         /* If no function was found */
      funcptr= dlsym(handle, in_string); /* Get function pointer */
      dlerr= dlerror();
    }

    if(dlerr==NULL) {           /* If a function was found */
      new_fvalue->type= func;   /* The new value is a function pointer */
      new_fvalue->content.ptr= funcptr; /* Store function pointer */
      (*new_symbol)->val= new_fvalue; /* Bind the symbol to the new
                                         function value */
    }

    free(mangled);
  }

  push_val(env, new_value);
  unprotect(new_value); unprotect(new_fvalue);
}

/* Print newline. */
extern void nl()
{
  printf("\n");
}

/* Gets the type of a value */
extern void type(environment *env)
{
  if(env->head->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  switch(CAR(env->head)->type){
  case empty:
    push_sym(env, "empty");
    break;
  case integer:
    push_sym(env, "integer");
    break;
  case tfloat:
    push_sym(env, "float");
    break;
  case string:
    push_sym(env, "string");
    break;
  case symb:
    push_sym(env, "symbol");
    break;
  case func:
    push_sym(env, "function");
    break;
  case tcons:
    push_sym(env, "pair");
    break;
  }
  swap(env);
  if (env->err) return;
  toss(env);
}    

/* Print a value */
void print_val(value *val, int noquote, stackitem *stack)
{
  stackitem *titem, *tstack;
  int depth;

  switch(val->type) {
  case empty:
    printf("[]");
    break;
  case integer:
    printf("%d", val->content.i);
    break;
  case tfloat:
    printf("%f", val->content.f);
    break;
  case string:
    if(noquote)
      printf("%s", (char*)(val->content.ptr));
    else
      printf("\"%s\"", (char*)(val->content.ptr));
    break;
  case symb:
    printf("%s", val->content.sym->id);
    break;
  case func:
    printf("#<function %p>", (funcp)(val->content.ptr));
    break;
  case tcons:
    printf("[ ");
    tstack= stack;
    do {
      titem=malloc(sizeof(stackitem));
      assert(titem != NULL);
      titem->item=val;
      titem->next=tstack;
      tstack=titem;             /* Put it on the stack */
      /* Search a stack of values being printed to see if we are already
         printing this value */
      titem=tstack;
      depth=0;
      while(titem != NULL && titem->item != CAR(val)){
        titem=titem->next;
        depth++;
      }
      if(titem != NULL){        /* If we found it on the stack, */
        printf("#%d#", depth);  /* print a depth reference */
      } else {
        print_val(CAR(val), noquote, tstack);
      }
      val= CDR(val);
      switch(val->type){
      case empty:
        break;
      case tcons:
        /* Search a stack of values being printed to see if we are already
           printing this value */
        titem=tstack;
        depth=0;
        while(titem != NULL && titem->item != val){
          titem=titem->next;
          depth++;
        }
        if(titem != NULL){      /* If we found it on the stack, */
          printf(" . #%d#", depth); /* print a depth reference */
        } else {
          printf(" ");
        }
        break;
      default:
        printf(" . ");          /* Improper list */
        print_val(val, noquote, tstack);
      }
    } while(val->type == tcons && titem == NULL);
    titem=tstack;
    while(titem != stack){
      tstack=titem->next;
      free(titem);
      titem=tstack;
    }
    printf(" ]");
    break;
  }
}

extern void print_(environment *env)
{
  if(env->head->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }
  print_val(CAR(env->head), 0, NULL);
  nl();
}

/* Prints the top element of the stack and then discards it. */
extern void print(environment *env)
{
  print_(env);
  if(env->err) return;
  toss(env);
}

extern void princ_(environment *env)
{
  if(env->head->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }
  print_val(CAR(env->head), 1, NULL);
}

/* Prints the top element of the stack and then discards it. */
extern void princ(environment *env)
{
  princ_(env);
  if(env->err) return;
  toss(env);
}

/* Only to be called by function printstack. */
void print_st(value *stack_head, long counter)
{ 
  if(CDR(stack_head)->type != empty)
    print_st(CDR(stack_head), counter+1);
  printf("%ld: ", counter);
  print_val(CAR(stack_head), 0, NULL);
  nl();
}

/* Prints the stack. */
extern void printstack(environment *env)
{
  if(env->head->type == empty) {
    printf("Stack Empty\n");
    return;
  }

  print_st(env->head, 1);
}

/* Swap the two top elements on the stack. */
extern void swap(environment *env)
{
  value *temp= env->head;
  
  if(env->head->type == empty || CDR(env->head)->type == empty) {
    printerr("Too Few Arguments");
    env->err=1;
    return;
  }

  env->head= CDR(env->head);
  CDR(temp)= CDR(env->head);
  CDR(env->head)= temp;
} 

/* Rotate the first three elements on the stack. */
extern void rot(environment *env)
{
  value *temp= env->head;
  
  if(env->head->type == empty || CDR(env->head)->type == empty
     || CDR(CDR(env->head))->type == empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }
  
  env->head= CDR(CDR(env->head));
  CDR(CDR(temp))= CDR(env->head);
  CDR(env->head)= temp;
}

/* Recall a value from a symbol, if bound */
extern void rcl(environment *env)
{
  value *val;

  if(env->head->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CAR(env->head)->type!=symb) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }

  val= CAR(env->head)->content.sym->val;
  if(val == NULL){
    printerr("Unbound Variable");
    env->err= 3;
    return;
  }
  push_val(env, val);           /* Return the symbol's bound value */
  swap(env);
  if(env->err) return;
  toss(env);                    /* toss the symbol */
  if(env->err) return;
}

/* If the top element is a symbol, determine if it's bound to a
   function value, and if it is, toss the symbol and execute the
   function. */
extern void eval(environment *env)
{
  funcp in_func;
  value* temp_val;
  value* iterator;

 eval_start:

  gc_maybe(env);

  if(env->head->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  switch(CAR(env->head)->type) {
    /* if it's a symbol */
  case symb:
    rcl(env);                   /* get its contents */
    if(env->err) return;
    if(CAR(env->head)->type!=symb){ /* don't recurse symbols */
      goto eval_start;
    }
    return;

    /* If it's a lone function value, run it */
  case func:
    in_func= (funcp)(CAR(env->head)->content.ptr);
    toss(env); 
    if(env->err) return;
    return in_func(env);

    /* If it's a list */
  case tcons:
    temp_val= CAR(env->head);
    protect(temp_val);

    toss(env); if(env->err) return;
    iterator= temp_val;
    
    while(iterator->type != empty) {
      push_val(env, CAR(iterator));
      
      if(CAR(env->head)->type==symb
         && CAR(env->head)->content.sym->id[0]==';') {
        toss(env);
        if(env->err) return;
        
        if(CDR(iterator)->type == empty){
          goto eval_start;
        }
        eval(env);
        if(env->err) return;
      }
      if (CDR(iterator)->type == empty || CDR(iterator)->type == tcons) 
        iterator= CDR(iterator);
      else {
        printerr("Bad Argument Type"); /* Improper list */
        env->err= 2;
        return;
      }
    }
    unprotect(temp_val);
    return;

  case empty:
  case integer:
  case tfloat:
  case string:
    return;
  }
}

/* Reverse (flip) a list */
extern void rev(environment *env)
{
  value *old_head, *new_head, *item;

  if(env->head->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CAR(env->head)->type==empty)
    return;                     /* Don't reverse an empty list */

  if(CAR(env->head)->type!=tcons) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }

  old_head= CAR(env->head);
  new_head= new_val(env);
  while(old_head->type != empty) {
    item= old_head;
    old_head= CDR(old_head);
    CDR(item)= new_head;
    new_head= item;
  }
  CAR(env->head)= new_head;
}

/* Make a list. */
extern void pack(environment *env)
{
  value *iterator, *temp, *ending;

  ending=new_val(env);

  iterator= env->head;
  if(iterator->type == empty
     || (CAR(iterator)->type==symb
     && CAR(iterator)->content.sym->id[0]=='[')) {
    temp= ending;
    toss(env);
  } else {
    /* Search for first delimiter */
    while(CDR(iterator)->type != empty
          && (CAR(CDR(iterator))->type!=symb
           || CAR(CDR(iterator))->content.sym->id[0]!='['))
      iterator= CDR(iterator);
    
    /* Extract list */
    temp= env->head;
    env->head= CDR(iterator);
    CDR(iterator)= ending;

    if(env->head->type != empty)
      toss(env);
  }

  /* Push list */

  push_val(env, temp);
  rev(env);
}

/* Relocate elements of the list on the stack. */
extern void expand(environment *env)
{
  value *temp, *new_head;

  /* Is top element a list? */
  if(env->head->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CAR(env->head)->type!=tcons) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }

  rev(env);

  if(env->err)
    return;

  /* The first list element is the new stack head */
  new_head= temp= CAR(env->head);

  toss(env);

  /* Find the end of the list */
  while(CDR(temp)->type != empty) {
    if (CDR(temp)->type == tcons)
      temp= CDR(temp);
    else {
      printerr("Bad Argument Type"); /* Improper list */
      env->err= 2;
      return;
    }
  }

  /* Connect the tail of the list with the old stack head */
  CDR(temp)= env->head;
  env->head= new_head;          /* ...and voila! */

}

/* Compares two elements by reference. */
extern void eq(environment *env)
{
  void *left, *right;

  if(env->head->type==empty || CDR(env->head)->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  left= CAR(env->head)->content.ptr;
  right= CAR(CDR(env->head))->content.ptr;
  toss(env); toss(env);

  push_int(env, left==right);
}

/* Negates the top element on the stack. */
extern void not(environment *env)
{
  int val;

  if(env->head->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CAR(env->head)->type!=integer) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }

  val= CAR(env->head)->content.i;
  toss(env);
  push_int(env, !val);
}

/* Compares the two top elements on the stack and return 0 if they're the
   same. */
extern void neq(environment *env)
{
  eq(env);
  not(env);
}

/* Give a symbol some content. */
extern void def(environment *env)
{
  symbol *sym;

  /* Needs two values on the stack, the top one must be a symbol */
  if(env->head->type==empty || CDR(env->head)->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CAR(env->head)->type!=symb) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }

  /* long names are a pain */
  sym= CAR(env->head)->content.ptr;

  /* Bind the symbol to the value */
  sym->val= CAR(CDR(env->head));

  toss(env); toss(env);
} 

/* Quit stack. */
extern void quit(environment *env)
{
  int i;

  clear(env);

  if (env->err) return;
  for(i= 0; i<HASHTBLSIZE; i++) {
    while(env->symbols[i]!= NULL) {
      forget_sym(&(env->symbols[i]));
    }
    env->symbols[i]= NULL;
  }

  env->gc_limit= 0;
  gc_maybe(env);

  words(env);

  if(env->free_string!=NULL)
    free(env->free_string);
  
#ifdef __linux__
  muntrace();
#endif

  exit(EXIT_SUCCESS);
}

/* Clear stack */
extern void clear(environment *env)
{
  while(env->head->type != empty)
    toss(env);
}

/* List all defined words */
extern void words(environment *env)
{
  symbol *temp;
  int i;
  
  for(i= 0; i<HASHTBLSIZE; i++) {
    temp= env->symbols[i];
    while(temp!=NULL) {
#ifdef DEBUG
      if (temp->val != NULL && temp->val->gc.flag.protect)
        printf("(protected) ");
#endif /* DEBUG */
      printf("%s\n", temp->id);
      temp= temp->next;
    }
  }
}

/* Internal forget function */
void forget_sym(symbol **hash_entry)
{
  symbol *temp;

  temp= *hash_entry;
  *hash_entry= (*hash_entry)->next;
  
  free(temp->id);
  free(temp);
}

/* Forgets a symbol (remove it from the hash table) */
extern void forget(environment *env)
{
  char* sym_id;

  if(env->head->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }
  
  if(CAR(env->head)->type!=symb) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }

  sym_id= CAR(env->head)->content.sym->id;
  toss(env);

  return forget_sym(hash(env->symbols, sym_id));
}

/* Returns the current error number to the stack */
extern void errn(environment *env)
{
  push_int(env, env->err);
}

int main(int argc, char **argv)
{
  environment myenv;

  int c;                        /* getopt option character */

#ifdef __linux__
  mtrace();
#endif

  init_env(&myenv);

  myenv.interactive = isatty(STDIN_FILENO) && isatty(STDOUT_FILENO);

  while ((c = getopt (argc, argv, "i")) != -1)
    switch (c)
      {
      case 'i':
        myenv.interactive = 1;
        break;
      case '?':
        fprintf (stderr,
                 "Unknown option character '\\x%x'.\n",
                 optopt);
        return EX_USAGE;
      default:
        abort ();
      }
  
  if (optind < argc) {
    myenv.interactive = 0;
    myenv.inputstream= fopen(argv[optind], "r");
    if(myenv.inputstream== NULL) {
      perror(argv[0]);
      exit (EX_NOINPUT);
    }
  }

  if(myenv.interactive) {
    printf("Stack version $Revision: 1.118 $\n\
Copyright (C) 2002  Mats Alritzson and Teddy Hogeborn\n\
Stack comes with ABSOLUTELY NO WARRANTY; for details type 'warranty;'.\n\
This is free software, and you are welcome to redistribute it\n\
under certain conditions; type 'copying;' for details.\n");
  }

  while(1) {
    if(myenv.in_string==NULL) {
      if (myenv.interactive) {
        if(myenv.err) {
          printf("(error %d)\n", myenv.err);
        }
        nl();
        printstack(&myenv);
        printf("> ");
      }
      myenv.err=0;
    }
    sx_72656164(&myenv);        /* "read" */
    if (myenv.err==4) {         /* EOF */
      myenv.err=0;
      quit(&myenv);
    } else if(myenv.head->type!=empty
              && CAR(myenv.head)->type==symb
              && CAR(myenv.head)->content.sym->id[0]
              ==';') {
      toss(&myenv);             /* No error check in main */
      eval(&myenv);
    }
    gc_maybe(&myenv);
  }
  quit(&myenv);
  return EXIT_FAILURE;
}

/* "+" */
extern void sx_2b(environment *env)
{
  int a, b;
  float fa, fb;
  size_t len;
  char* new_string;
  value *a_val, *b_val;

  if(env->head->type==empty || CDR(env->head)->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CAR(env->head)->type==string
     && CAR(CDR(env->head))->type==string) {
    a_val= CAR(env->head);
    b_val= CAR(CDR(env->head));
    protect(a_val); protect(b_val);
    toss(env); if(env->err) return;
    toss(env); if(env->err) return;
    len= strlen(a_val->content.ptr)+strlen(b_val->content.ptr)+1;
    new_string= malloc(len);
    assert(new_string != NULL);
    strcpy(new_string, b_val->content.ptr);
    strcat(new_string, a_val->content.ptr);
    push_cstring(env, new_string);
    unprotect(a_val); unprotect(b_val);
    free(new_string);
    
    return;
  }
  
  if(CAR(env->head)->type==integer
     && CAR(CDR(env->head))->type==integer) {
    a= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    b= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    push_int(env, b+a);

    return;
  }

  if(CAR(env->head)->type==tfloat
     && CAR(CDR(env->head))->type==tfloat) {
    fa= CAR(env->head)->content.f;
    toss(env); if(env->err) return;
    fb= CAR(env->head)->content.f;
    toss(env); if(env->err) return;
    push_float(env, fb+fa);
    
    return;
  }

  if(CAR(env->head)->type==tfloat
     && CAR(CDR(env->head))->type==integer) {
    fa= CAR(env->head)->content.f;
    toss(env); if(env->err) return;
    b= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    push_float(env, b+fa);
    
    return;
  }

  if(CAR(env->head)->type==integer
     && CAR(CDR(env->head))->type==tfloat) {
    a= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    fb= CAR(env->head)->content.f;
    toss(env); if(env->err) return;
    push_float(env, fb+a);

    return;
  }

  printerr("Bad Argument Type");
  env->err=2;
}

/* "-" */
extern void sx_2d(environment *env)
{
  int a, b;
  float fa, fb;

  if(env->head->type==empty || CDR(env->head)->type==empty) {
    printerr("Too Few Arguments");
    env->err=1;
    return;
  }
  
  if(CAR(env->head)->type==integer
     && CAR(CDR(env->head))->type==integer) {
    a= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    b= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    push_int(env, b-a);

    return;
  }

  if(CAR(env->head)->type==tfloat
     && CAR(CDR(env->head))->type==tfloat) {
    fa= CAR(env->head)->content.f;
    toss(env); if(env->err) return;
    fb= CAR(env->head)->content.f;
    toss(env); if(env->err) return;
    push_float(env, fb-fa);
    
    return;
  }

  if(CAR(env->head)->type==tfloat
     && CAR(CDR(env->head))->type==integer) {
    fa= CAR(env->head)->content.f;
    toss(env); if(env->err) return;
    b= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    push_float(env, b-fa);
    
    return;
  }

  if(CAR(env->head)->type==integer
     && CAR(CDR(env->head))->type==tfloat) {
    a= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    fb= CAR(env->head)->content.f;
    toss(env); if(env->err) return;
    push_float(env, fb-a);

    return;
  }

  printerr("Bad Argument Type");
  env->err=2;
}

/* ">" */
extern void sx_3e(environment *env)
{
  int a, b;
  float fa, fb;

  if(env->head->type==empty || CDR(env->head)->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }
  
  if(CAR(env->head)->type==integer
     && CAR(CDR(env->head))->type==integer) {
    a= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    b= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    push_int(env, b>a);

    return;
  }

  if(CAR(env->head)->type==tfloat
     && CAR(CDR(env->head))->type==tfloat) {
    fa= CAR(env->head)->content.f;
    toss(env); if(env->err) return;
    fb= CAR(env->head)->content.f;
    toss(env); if(env->err) return;
    push_int(env, fb>fa);
    
    return;
  }

  if(CAR(env->head)->type==tfloat
     && CAR(CDR(env->head))->type==integer) {
    fa= CAR(env->head)->content.f;
    toss(env); if(env->err) return;
    b= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    push_int(env, b>fa);
    
    return;
  }

  if(CAR(env->head)->type==integer
     && CAR(CDR(env->head))->type==tfloat) {
    a= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    fb= CAR(env->head)->content.f;
    toss(env); if(env->err) return;
    push_int(env, fb>a);

    return;
  }

  printerr("Bad Argument Type");
  env->err= 2;
}

/* "<" */
extern void sx_3c(environment *env) 
{
  swap(env); if(env->err) return;
  sx_3e(env);
}

/* "<=" */
extern void sx_3c3d(environment *env)
{
  sx_3e(env); if(env->err) return;
  not(env);
}

/* ">=" */
extern void sx_3e3d(environment *env)
{
  sx_3c(env); if(env->err) return;
  not(env);
}

/* Return copy of a value */
value *copy_val(environment *env, value *old_value)
{
  value *new_value;

  if(old_value==NULL)
    return NULL;

  protect(old_value);
  new_value= new_val(env);
  new_value->type= old_value->type;

  switch(old_value->type){
  case tfloat:
  case integer:
  case func:
  case symb:
  case empty:
    new_value->content= old_value->content;
    break;
  case string:
    (char *)(new_value->content.ptr)= 
      strdup((char *)(old_value->content.ptr));
    break;
  case tcons:

    new_value->content.c= malloc(sizeof(pair));
    assert(new_value->content.c!=NULL);
    env->gc_count += sizeof(pair);

    CAR(new_value)= copy_val(env, CAR(old_value)); /* recurse */
    CDR(new_value)= copy_val(env, CDR(old_value)); /* recurse */
    break;
  }

  unprotect(old_value);

  return new_value;
}

/* "dup"; duplicates an item on the stack */
extern void sx_647570(environment *env)
{
  if(env->head->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }
  push_val(env, copy_val(env, CAR(env->head)));
}

/* "if", If-Then */
extern void sx_6966(environment *env)
{
  int truth;

  if(env->head->type==empty || CDR(env->head)->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CAR(CDR(env->head))->type != integer) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }
  
  swap(env);
  if(env->err) return;
  
  truth= CAR(env->head)->content.i;

  toss(env);
  if(env->err) return;

  if(truth)
    eval(env);
  else
    toss(env);
}

/* If-Then-Else */
extern void ifelse(environment *env)
{
  int truth;

  if(env->head->type==empty || CDR(env->head)->type==empty
     || CDR(CDR(env->head))->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CAR(CDR(CDR(env->head)))->type!=integer) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }
  
  rot(env);
  if(env->err) return;
  
  truth= CAR(env->head)->content.i;

  toss(env);
  if(env->err) return;

  if(!truth)
    swap(env);
  if(env->err) return;

  toss(env);
  if(env->err) return;

  eval(env);
}

extern void sx_656c7365(environment *env)
{
  if(env->head->type==empty || CDR(env->head)->type==empty 
     || CDR(CDR(env->head))->type==empty || CDR(CDR(CDR(env->head)))->type==empty
     || CDR(CDR(CDR(CDR(env->head))))->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CAR(CDR(env->head))->type!=symb
     || strcmp(CAR(CDR(env->head))->content.sym->id, "then")!=0
     || CAR(CDR(CDR(CDR(env->head))))->type!=symb
     || strcmp(CAR(CDR(CDR(CDR(env->head))))->content.sym->id, "if")!=0) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }

  swap(env); toss(env); rot(env); toss(env);
  ifelse(env);
}

extern void then(environment *env)
{
  if(env->head->type==empty || CDR(env->head)->type==empty
     || CDR(CDR(env->head))->type==empty) { 
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CAR(CDR(env->head))->type!=symb
     || strcmp(CAR(CDR(env->head))->content.sym->id, "if")!=0) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }

  swap(env); toss(env);
  sx_6966(env);
}

/* "while" */
extern void sx_7768696c65(environment *env)
{
  int truth;
  value *loop, *test;

  if(env->head->type==empty || CDR(env->head)->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  loop= CAR(env->head);
  protect(loop);
  toss(env); if(env->err) return;

  test= CAR(env->head);
  protect(test);
  toss(env); if(env->err) return;

  do {
    push_val(env, test);
    eval(env);
    
    if(CAR(env->head)->type != integer) {
      printerr("Bad Argument Type");
      env->err= 2;
      return;
    }
    
    truth= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    
    if(truth) {
      push_val(env, loop);
      eval(env);
    } else {
      toss(env);
    }
  
  } while(truth);

  unprotect(loop); unprotect(test);
}


/* "for"; for-loop */
extern void sx_666f72(environment *env)
{
  value *loop;
  int foo1, foo2;

  if(env->head->type==empty || CDR(env->head)->type==empty 
     || CDR(CDR(env->head))->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CAR(CDR(env->head))->type!=integer
     || CAR(CDR(CDR(env->head)))->type!=integer) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }

  loop= CAR(env->head);
  protect(loop);
  toss(env); if(env->err) return;

  foo2= CAR(env->head)->content.i;
  toss(env); if(env->err) return;

  foo1= CAR(env->head)->content.i;
  toss(env); if(env->err) return;

  if(foo1<=foo2) {
    while(foo1<=foo2) {
      push_int(env, foo1);
      push_val(env, loop);
      eval(env); if(env->err) return;
      foo1++;
    }
  } else {
    while(foo1>=foo2) {
      push_int(env, foo1);
      push_val(env, loop);
      eval(env); if(env->err) return;
      foo1--;
    }
  }
  unprotect(loop);
}

/* Variant of for-loop */
extern void foreach(environment *env)
{  
  value *loop, *foo;
  value *iterator;
  
  if(env->head->type==empty || CDR(env->head)->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CAR(CDR(env->head))->type!=tcons) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }

  loop= CAR(env->head);
  protect(loop);
  toss(env); if(env->err) return;

  foo= CAR(env->head);
  protect(foo);
  toss(env); if(env->err) return;

  iterator= foo;

  while(iterator!=NULL) {
    push_val(env, CAR(iterator));
    push_val(env, loop);
    eval(env); if(env->err) return;
    if (iterator->type == tcons){
      iterator= CDR(iterator);
    } else {
      printerr("Bad Argument Type"); /* Improper list */
      env->err= 2;
      break;
    }
  }
  unprotect(loop); unprotect(foo);
}

/* "to" */
extern void to(environment *env)
{
  int ending, start, i;
  value *iterator, *temp;

  if(env->head->type==empty || CDR(env->head)->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CAR(env->head)->type!=integer 
     || CAR(CDR(env->head))->type!=integer) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }

  ending= CAR(env->head)->content.i;
  toss(env); if(env->err) return;
  start= CAR(env->head)->content.i;
  toss(env); if(env->err) return;

  push_sym(env, "[");

  if(ending>=start) {
    for(i= ending; i>=start; i--)
      push_int(env, i);
  } else {
    for(i= ending; i<=start; i++)
      push_int(env, i);
  }

  iterator= env->head;

  if(iterator->type==empty
     || (CAR(iterator)->type==symb
         && CAR(iterator)->content.sym->id[0]=='[')) {
    temp= NULL;
    toss(env);
  } else {
    /* Search for first delimiter */
    while(CDR(iterator)!=NULL 
          && (CAR(CDR(iterator))->type!=symb
              || CAR(CDR(iterator))->content.sym->id[0]!='['))
      iterator= CDR(iterator);
    
    /* Extract list */
    temp= env->head;
    env->head= CDR(iterator);
    CDR(iterator)= NULL;

    if(env->head!=NULL)
      toss(env);
  }

  /* Push list */
  push_val(env, temp);
}

/* Read a string */
extern void readline(environment *env)
{
  char in_string[101];

  if(fgets(in_string, 100, env->inputstream)==NULL)
    push_cstring(env, "");
  else
    push_cstring(env, in_string);
}

/* "read"; Read a value and place on stack */
extern void sx_72656164(environment *env)
{
  const char symbform[]= "%[a-zA-Z0-9!$%*+./:<=>?@^_~-]%n";
  const char strform[]= "\"%[^\"]\"%n";
  const char intform[]= "%i%n";
  const char fltform[]= "%f%n";
  const char blankform[]= "%*[ \t]%n";
  const char ebrackform[]= "]%n";
  const char semicform[]= ";%n";
  const char bbrackform[]= "[%n";

  int itemp, readlength= -1;
  int count= -1;
  float ftemp;
  static int depth= 0;
  char *match;
  size_t inlength;

  if(env->in_string==NULL) {
    if(depth > 0 && env->interactive) {
      printf("]> ");
    }
    readline(env); if(env->err) return;

    if(((char *)(CAR(env->head)->content.ptr))[0]=='\0'){
      env->err= 4;              /* "" means EOF */
      return;
    }
    
    env->in_string= malloc(strlen(CAR(env->head)->content.ptr)+1);
    assert(env->in_string != NULL);
    env->free_string= env->in_string; /* Save the original pointer */
    strcpy(env->in_string, CAR(env->head)->content.ptr);
    toss(env); if(env->err) return;
  }
  
  inlength= strlen(env->in_string)+1;
  match= malloc(inlength);
  assert(match != NULL);

  if(sscanf(env->in_string, blankform, &readlength) != EOF
     && readlength != -1) {
    ; 
  } else if(sscanf(env->in_string, fltform, &ftemp, &readlength) != EOF
            && readlength != -1) {
    if(sscanf(env->in_string, intform, &itemp, &count) != EOF
       && count==readlength) {
      push_int(env, itemp);
    } else {
      push_float(env, ftemp);
    }
  } else if(sscanf(env->in_string, "\"\"%n", &readlength) != EOF
            && readlength != -1) {
    push_cstring(env, "");
  } else if(sscanf(env->in_string, strform, match, &readlength) != EOF
            && readlength != -1) {
    push_cstring(env, match);
  } else if(sscanf(env->in_string, symbform, match, &readlength) != EOF
            && readlength != -1) {
    push_sym(env, match);
  } else if(sscanf(env->in_string, ebrackform, &readlength) != EOF
            && readlength != -1) {
    pack(env); if(env->err) return;
    if(depth != 0) depth--;
  } else if(sscanf(env->in_string, semicform, &readlength) != EOF
            && readlength != -1) {
    push_sym(env, ";");
  } else if(sscanf(env->in_string, bbrackform, &readlength) != EOF
            && readlength != -1) {
    push_sym(env, "[");
    depth++;
  } else {
    free(env->free_string);
    env->in_string = env->free_string = NULL;
  }
  if (env->in_string != NULL) {
    env->in_string += readlength;
  }

  free(match);

  if(depth)
    return sx_72656164(env);
}

#ifdef __linux__
extern void beep(environment *env)
{
  int freq, dur, period, ticks;

  if(env->head->type==empty || CDR(env->head)->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CAR(env->head)->type!=integer
     || CAR(CDR(env->head))->type!=integer) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }

  dur= CAR(env->head)->content.i;
  toss(env);
  freq= CAR(env->head)->content.i;
  toss(env);

  period= 1193180/freq;         /* convert freq from Hz to period
                                   length */
  ticks= dur*.001193180;        /* convert duration from µseconds to
                                   timer ticks */

/*    ticks=dur/1000; */

      /*  if (ioctl(STDOUT_FILENO, KDMKTONE, (125<<16) + 0x637)==0) */
  switch (ioctl(STDOUT_FILENO, KDMKTONE, (ticks<<16) | period)){
  case 0:
    usleep(dur);
    return;
  case -1:
    perror("beep");
    env->err= 5;
    return;
  default:
    abort();
  }
}
#endif /* __linux__ */

/* "wait" */
extern void sx_77616974(environment *env)
{
  int dur;

  if(env->head->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CAR(env->head)->type!=integer) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }

  dur= CAR(env->head)->content.i;
  toss(env);

  usleep(dur);
}

extern void copying(environment *env)
{
  printf("                  GNU GENERAL PUBLIC LICENSE\n\
                       Version 2, June 1991\n\
\n\
 Copyright (C) 1989, 1991 Free Software Foundation, Inc.\n\
     59 Temple Place, Suite 330, Boston, MA  02111-1307  USA\n\
 Everyone is permitted to copy and distribute verbatim copies\n\
 of this license document, but changing it is not allowed.\n\
\n\
                            Preamble\n\
\n\
  The licenses for most software are designed to take away your\n\
freedom to share and change it.  By contrast, the GNU General Public\n\
License is intended to guarantee your freedom to share and change free\n\
software--to make sure the software is free for all its users.  This\n\
General Public License applies to most of the Free Software\n\
Foundation's software and to any other program whose authors commit to\n\
using it.  (Some other Free Software Foundation software is covered by\n\
the GNU Library General Public License instead.)  You can apply it to\n\
your programs, too.\n\
\n\
  When we speak of free software, we are referring to freedom, not\n\
price.  Our General Public Licenses are designed to make sure that you\n\
have the freedom to distribute copies of free software (and charge for\n\
this service if you wish), that you receive source code or can get it\n\
if you want it, that you can change the software or use pieces of it\n\
in new free programs; and that you know you can do these things.\n\
\n\
  To protect your rights, we need to make restrictions that forbid\n\
anyone to deny you these rights or to ask you to surrender the rights.\n\
These restrictions translate to certain responsibilities for you if you\n\
distribute copies of the software, or if you modify it.\n\
\n\
  For example, if you distribute copies of such a program, whether\n\
gratis or for a fee, you must give the recipients all the rights that\n\
you have.  You must make sure that they, too, receive or can get the\n\
source code.  And you must show them these terms so they know their\n\
rights.\n\
\n\
  We protect your rights with two steps: (1) copyright the software, and\n\
(2) offer you this license which gives you legal permission to copy,\n\
distribute and/or modify the software.\n\
\n\
  Also, for each author's protection and ours, we want to make certain\n\
that everyone understands that there is no warranty for this free\n\
software.  If the software is modified by someone else and passed on, we\n\
want its recipients to know that what they have is not the original, so\n\
that any problems introduced by others will not reflect on the original\n\
authors' reputations.\n\
\n\
  Finally, any free program is threatened constantly by software\n\
patents.  We wish to avoid the danger that redistributors of a free\n\
program will individually obtain patent licenses, in effect making the\n\
program proprietary.  To prevent this, we have made it clear that any\n\
patent must be licensed for everyone's free use or not licensed at all.\n\
\n\
  The precise terms and conditions for copying, distribution and\n\
modification follow.\n\
\n\
                    GNU GENERAL PUBLIC LICENSE\n\
   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION\n\
\n\
  0. This License applies to any program or other work which contains\n\
a notice placed by the copyright holder saying it may be distributed\n\
under the terms of this General Public License.  The \"Program\", below,\n\
refers to any such program or work, and a \"work based on the Program\"\n\
means either the Program or any derivative work under copyright law:\n\
that is to say, a work containing the Program or a portion of it,\n\
either verbatim or with modifications and/or translated into another\n\
language.  (Hereinafter, translation is included without limitation in\n\
the term \"modification\".)  Each licensee is addressed as \"you\".\n\
\n\
Activities other than copying, distribution and modification are not\n\
covered by this License; they are outside its scope.  The act of\n\
running the Program is not restricted, and the output from the Program\n\
is covered only if its contents constitute a work based on the\n\
Program (independent of having been made by running the Program).\n\
Whether that is true depends on what the Program does.\n\
\n\
  1. You may copy and distribute verbatim copies of the Program's\n\
source code as you receive it, in any medium, provided that you\n\
conspicuously and appropriately publish on each copy an appropriate\n\
copyright notice and disclaimer of warranty; keep intact all the\n\
notices that refer to this License and to the absence of any warranty;\n\
and give any other recipients of the Program a copy of this License\n\
along with the Program.\n\
\n\
You may charge a fee for the physical act of transferring a copy, and\n\
you may at your option offer warranty protection in exchange for a fee.\n\
\n\
  2. You may modify your copy or copies of the Program or any portion\n\
of it, thus forming a work based on the Program, and copy and\n\
distribute such modifications or work under the terms of Section 1\n\
above, provided that you also meet all of these conditions:\n\
\n\
    a) You must cause the modified files to carry prominent notices\n\
    stating that you changed the files and the date of any change.\n\
\n\
    b) You must cause any work that you distribute or publish, that in\n\
    whole or in part contains or is derived from the Program or any\n\
    part thereof, to be licensed as a whole at no charge to all third\n\
    parties under the terms of this License.\n\
\n\
    c) If the modified program normally reads commands interactively\n\
    when run, you must cause it, when started running for such\n\
    interactive use in the most ordinary way, to print or display an\n\
    announcement including an appropriate copyright notice and a\n\
    notice that there is no warranty (or else, saying that you provide\n\
    a warranty) and that users may redistribute the program under\n\
    these conditions, and telling the user how to view a copy of this\n\
    License.  (Exception: if the Program itself is interactive but\n\
    does not normally print such an announcement, your work based on\n\
    the Program is not required to print an announcement.)\n\
\n\
These requirements apply to the modified work as a whole.  If\n\
identifiable sections of that work are not derived from the Program,\n\
and can be reasonably considered independent and separate works in\n\
themselves, then this License, and its terms, do not apply to those\n\
sections when you distribute them as separate works.  But when you\n\
distribute the same sections as part of a whole which is a work based\n\
on the Program, the distribution of the whole must be on the terms of\n\
this License, whose permissions for other licensees extend to the\n\
entire whole, and thus to each and every part regardless of who wrote it.\n\
\n\
Thus, it is not the intent of this section to claim rights or contest\n\
your rights to work written entirely by you; rather, the intent is to\n\
exercise the right to control the distribution of derivative or\n\
collective works based on the Program.\n\
\n\
In addition, mere aggregation of another work not based on the Program\n\
with the Program (or with a work based on the Program) on a volume of\n\
a storage or distribution medium does not bring the other work under\n\
the scope of this License.\n\
\n\
  3. You may copy and distribute the Program (or a work based on it,\n\
under Section 2) in object code or executable form under the terms of\n\
Sections 1 and 2 above provided that you also do one of the following:\n\
\n\
    a) Accompany it with the complete corresponding machine-readable\n\
    source code, which must be distributed under the terms of Sections\n\
    1 and 2 above on a medium customarily used for software interchange; or,\n\
\n\
    b) Accompany it with a written offer, valid for at least three\n\
    years, to give any third party, for a charge no more than your\n\
    cost of physically performing source distribution, a complete\n\
    machine-readable copy of the corresponding source code, to be\n\
    distributed under the terms of Sections 1 and 2 above on a medium\n\
    customarily used for software interchange; or,\n\
\n\
    c) Accompany it with the information you received as to the offer\n\
    to distribute corresponding source code.  (This alternative is\n\
    allowed only for noncommercial distribution and only if you\n\
    received the program in object code or executable form with such\n\
    an offer, in accord with Subsection b above.)\n\
\n\
The source code for a work means the preferred form of the work for\n\
making modifications to it.  For an executable work, complete source\n\
code means all the source code for all modules it contains, plus any\n\
associated interface definition files, plus the scripts used to\n\
control compilation and installation of the executable.  However, as a\n\
special exception, the source code distributed need not include\n\
anything that is normally distributed (in either source or binary\n\
form) with the major components (compiler, kernel, and so on) of the\n\
operating system on which the executable runs, unless that component\n\
itself accompanies the executable.\n\
\n\
If distribution of executable or object code is made by offering\n\
access to copy from a designated place, then offering equivalent\n\
access to copy the source code from the same place counts as\n\
distribution of the source code, even though third parties are not\n\
compelled to copy the source along with the object code.\n\
\n\
  4. You may not copy, modify, sublicense, or distribute the Program\n\
except as expressly provided under this License.  Any attempt\n\
otherwise to copy, modify, sublicense or distribute the Program is\n\
void, and will automatically terminate your rights under this License.\n\
However, parties who have received copies, or rights, from you under\n\
this License will not have their licenses terminated so long as such\n\
parties remain in full compliance.\n\
\n\
  5. You are not required to accept this License, since you have not\n\
signed it.  However, nothing else grants you permission to modify or\n\
distribute the Program or its derivative works.  These actions are\n\
prohibited by law if you do not accept this License.  Therefore, by\n\
modifying or distributing the Program (or any work based on the\n\
Program), you indicate your acceptance of this License to do so, and\n\
all its terms and conditions for copying, distributing or modifying\n\
the Program or works based on it.\n\
\n\
  6. Each time you redistribute the Program (or any work based on the\n\
Program), the recipient automatically receives a license from the\n\
original licensor to copy, distribute or modify the Program subject to\n\
these terms and conditions.  You may not impose any further\n\
restrictions on the recipients' exercise of the rights granted herein.\n\
You are not responsible for enforcing compliance by third parties to\n\
this License.\n\
\n\
  7. If, as a consequence of a court judgment or allegation of patent\n\
infringement or for any other reason (not limited to patent issues),\n\
conditions are imposed on you (whether by court order, agreement or\n\
otherwise) that contradict the conditions of this License, they do not\n\
excuse you from the conditions of this License.  If you cannot\n\
distribute so as to satisfy simultaneously your obligations under this\n\
License and any other pertinent obligations, then as a consequence you\n\
may not distribute the Program at all.  For example, if a patent\n\
license would not permit royalty-free redistribution of the Program by\n\
all those who receive copies directly or indirectly through you, then\n\
the only way you could satisfy both it and this License would be to\n\
refrain entirely from distribution of the Program.\n\
\n\
If any portion of this section is held invalid or unenforceable under\n\
any particular circumstance, the balance of the section is intended to\n\
apply and the section as a whole is intended to apply in other\n\
circumstances.\n\
\n\
It is not the purpose of this section to induce you to infringe any\n\
patents or other property right claims or to contest validity of any\n\
such claims; this section has the sole purpose of protecting the\n\
integrity of the free software distribution system, which is\n\
implemented by public license practices.  Many people have made\n\
generous contributions to the wide range of software distributed\n\
through that system in reliance on consistent application of that\n\
system; it is up to the author/donor to decide if he or she is willing\n\
to distribute software through any other system and a licensee cannot\n\
impose that choice.\n\
\n\
This section is intended to make thoroughly clear what is believed to\n\
be a consequence of the rest of this License.\n\
\n\
  8. If the distribution and/or use of the Program is restricted in\n\
certain countries either by patents or by copyrighted interfaces, the\n\
original copyright holder who places the Program under this License\n\
may add an explicit geographical distribution limitation excluding\n\
those countries, so that distribution is permitted only in or among\n\
countries not thus excluded.  In such case, this License incorporates\n\
the limitation as if written in the body of this License.\n\
\n\
  9. The Free Software Foundation may publish revised and/or new versions\n\
of the General Public License from time to time.  Such new versions will\n\
be similar in spirit to the present version, but may differ in detail to\n\
address new problems or concerns.\n\
\n\
Each version is given a distinguishing version number.  If the Program\n\
specifies a version number of this License which applies to it and \"any\n\
later version\", you have the option of following the terms and conditions\n\
either of that version or of any later version published by the Free\n\
Software Foundation.  If the Program does not specify a version number of\n\
this License, you may choose any version ever published by the Free Software\n\
Foundation.\n\
\n\
  10. If you wish to incorporate parts of the Program into other free\n\
programs whose distribution conditions are different, write to the author\n\
to ask for permission.  For software which is copyrighted by the Free\n\
Software Foundation, write to the Free Software Foundation; we sometimes\n\
make exceptions for this.  Our decision will be guided by the two goals\n\
of preserving the free status of all derivatives of our free software and\n\
of promoting the sharing and reuse of software generally.\n");
}

extern void warranty(environment *env)
{
  printf("                          NO WARRANTY\n\
\n\
  11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY\n\
FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN\n\
OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES\n\
PROVIDE THE PROGRAM \"AS IS\" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED\n\
OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF\n\
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS\n\
TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE\n\
PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,\n\
REPAIR OR CORRECTION.\n\
\n\
  12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING\n\
WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR\n\
REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,\n\
INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING\n\
OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED\n\
TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY\n\
YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER\n\
PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE\n\
POSSIBILITY OF SUCH DAMAGES.\n");
}

/* "*" */
extern void sx_2a(environment *env)
{
  int a, b;
  float fa, fb;

  if(env->head->type==empty || CDR(env->head)->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }
  
  if(CAR(env->head)->type==integer
     && CAR(CDR(env->head))->type==integer) {
    a= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    b= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    push_int(env, b*a);

    return;
  }

  if(CAR(env->head)->type==tfloat
     && CAR(CDR(env->head))->type==tfloat) {
    fa= CAR(env->head)->content.f;
    toss(env); if(env->err) return;
    fb= CAR(env->head)->content.f;
    toss(env); if(env->err) return;
    push_float(env, fb*fa);
    
    return;
  }

  if(CAR(env->head)->type==tfloat
     && CAR(CDR(env->head))->type==integer) {
    fa= CAR(env->head)->content.f;
    toss(env); if(env->err) return;
    b= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    push_float(env, b*fa);
    
    return;
  }

  if(CAR(env->head)->type==integer
     && CAR(CDR(env->head))->type==tfloat) {
    a= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    fb= CAR(env->head)->content.f;
    toss(env); if(env->err) return;
    push_float(env, fb*a);

    return;
  }

  printerr("Bad Argument Type");
  env->err= 2;
}

/* "/" */
extern void sx_2f(environment *env)
{
  int a, b;
  float fa, fb;

  if(env->head->type==empty || CDR(env->head)->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }
  
  if(CAR(env->head)->type==integer
     && CAR(CDR(env->head))->type==integer) {
    a= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    b= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    push_float(env, b/a);

    return;
  }

  if(CAR(env->head)->type==tfloat
     && CAR(CDR(env->head))->type==tfloat) {
    fa= CAR(env->head)->content.f;
    toss(env); if(env->err) return;
    fb= CAR(env->head)->content.f;
    toss(env); if(env->err) return;
    push_float(env, fb/fa);
    
    return;
  }

  if(CAR(env->head)->type==tfloat
     && CAR(CDR(env->head))->type==integer) {
    fa= CAR(env->head)->content.f;
    toss(env); if(env->err) return;
    b= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    push_float(env, b/fa);
    
    return;
  }

  if(CAR(env->head)->type==integer
     && CAR(CDR(env->head))->type==tfloat) {
    a= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    fb= CAR(env->head)->content.f;
    toss(env); if(env->err) return;
    push_float(env, fb/a);

    return;
  }

  printerr("Bad Argument Type");
  env->err= 2;
}

/* "mod" */
extern void mod(environment *env)
{
  int a, b;

  if(env->head->type==empty || CDR(env->head)->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }
  
  if(CAR(env->head)->type==integer
     && CAR(CDR(env->head))->type==integer) {
    a= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    b= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    push_int(env, b%a);

    return;
  }

  printerr("Bad Argument Type");
  env->err= 2;
}

/* "div" */
extern void sx_646976(environment *env)
{
  int a, b;
  
  if(env->head->type==empty || CDR(env->head)->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CAR(env->head)->type==integer
     && CAR(CDR(env->head))->type==integer) {
    a= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    b= CAR(env->head)->content.i;
    toss(env); if(env->err) return;
    push_int(env, (int)b/a);

    return;
  }

  printerr("Bad Argument Type");
  env->err= 2;
}

extern void setcar(environment *env)
{
  if(env->head->type==empty || CDR(env->head)->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CDR(env->head)->type!=tcons) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }

  CAR(CAR(CDR(env->head)))=CAR(env->head);
  toss(env);
}

extern void setcdr(environment *env)
{
  if(env->head->type==empty || CDR(env->head)->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CDR(env->head)->type!=tcons) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }

  CDR(CAR(CDR(env->head)))=CAR(env->head);
  toss(env);
}

extern void car(environment *env)
{
  if(env->head->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CAR(env->head)->type!=tcons) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }

  CAR(env->head)=CAR(CAR(env->head));
}

extern void cdr(environment *env)
{
  if(env->head->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CAR(env->head)->type!=tcons) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }

  CAR(env->head)=CDR(CAR(env->head));
}

extern void cons(environment *env)
{
  value *val;

  if(env->head->type==empty || CDR(env->head)->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  val=new_val(env);
  val->content.c= malloc(sizeof(pair));
  assert(val->content.c!=NULL);

  env->gc_count += sizeof(pair);
  val->type=tcons;

  CAR(val)= CAR(CDR(env->head));
  CDR(val)= CAR(env->head);

  push_val(env, val);

  swap(env); if(env->err) return;
  toss(env); if(env->err) return;
  swap(env); if(env->err) return;
  toss(env); if(env->err) return;
}

/*  2: 3                        =>                */
/*  1: [ [ 1 . 2 ] [ 3 . 4 ] ]  =>  1: [ 3 . 4 ]  */
extern void assq(environment *env)
{
  value *key, *item;

  /* Needs two values on the stack, the top one must be an association
     list */
  if(env->head->type==empty || CDR(env->head)->type==empty) {
    printerr("Too Few Arguments");
    env->err= 1;
    return;
  }

  if(CAR(env->head)->type!=tcons) {
    printerr("Bad Argument Type");
    env->err= 2;
    return;
  }

  key=CAR(CDR(env->head));
  item=CAR(env->head);

  while(item->type == tcons){
    if(CAR(item)->type != tcons){
      printerr("Bad Argument Type");
      env->err= 2;
      return;
    }
    push_val(env, key);
    push_val(env, CAR(CAR(item)));
    eq(env); if(env->err) return;
    
    if(CAR(env->head)->content.i){
      toss(env);
      break;
    }
    toss(env);
    item=CDR(item);
  }

  if(item->type == tcons){      /* A match was found */
    push_val(env, CAR(item));
  } else {
    push_int(env, 0);
  }
  swap(env); if(env->err) return;
  toss(env); if(env->err) return;
  swap(env); if(env->err) return;
  toss(env);
}