cvs/stack/stack.c

/* printf */
#include <stdio.h>
/* EXIT_SUCCESS */
#include <stdlib.h>
/* NULL */
#include <stddef.h>
/* dlopen, dlsym, dlerror */
#include <dlfcn.h>
/* assert */
#include <assert.h>

#define HASHTBLSIZE 65536

typedef struct stack_item
{
  enum {
    value,                      /* Integer */
    string,
    ref,                        /* Reference (to an element in the
                                   hash table) */
    func,                       /* Function pointer */
    symbol, 
    list
  } type;                       /* Type of stack element */

  union {
    void* ptr;                  /* Pointer to the content */
    int val;                    /* ...or an integer */
  } content;                    /* Stores a pointer or an integer */

  char* id;                     /* Symbol name */
  struct stack_item* next;      /* Next element */
} stackitem;


typedef stackitem* hashtbl[HASHTBLSIZE]; /* Hash table declaration */
typedef void (*funcp)(stackitem**); /* funcp is a pointer to a
                                       void function (stackitem **) */

/* Initialize a newly created hash table. */
void init_hashtbl(hashtbl out_hash)
{
  long i;

  for(i= 0; i<HASHTBLSIZE; i++)
    out_hash[i]= NULL;
}

/* Returns a pointer to an element in the hash table. */
stackitem** hash(hashtbl in_hashtbl, const char* in_string)
{
  long i= 0;
  unsigned long out_hash= 0;
  char key= '\0';
  stackitem** 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(position != NULL){
    if(*position==NULL)         /* If empty */
      return position;
    
    if(strcmp(in_string, (*position)->id)==0) /* If match */
      return position;

    position= &((*position)->next); /* Try next */
  }
  return NULL;                  /* end of list reached without finding
                                   an empty position */
}

/* Generic push function. */
int push(stackitem** stack_head, stackitem* in_item)
{
  in_item->next= *stack_head;
  *stack_head= in_item;
  return 1;
}

/* Push a value on the stack. */
int push_val(stackitem** stack_head, int in_val) 
{
  stackitem* new_item= malloc(sizeof(stackitem));
  assert(new_item != NULL);
  new_item->content.val= in_val;
  new_item->type= value;

  push(stack_head, new_item);
  return 1;
}

/* Copy a string onto the stack. */
int push_cstring(stackitem** stack_head, const char* in_string)
{
  stackitem* new_item= malloc(sizeof(stackitem));
  new_item->content.ptr= malloc(strlen(in_string)+1);
  strcpy(new_item->content.ptr, in_string);
  new_item->type= string;

  push(stack_head, new_item);
  return 1;
}

/* Create a new hash entry. */
int mk_hashentry(hashtbl in_hashtbl, stackitem* in_item, const char* id)
{
  in_item->id= malloc(strlen(id)+1);

  strcpy(in_item->id, id);
  push(hash(in_hashtbl, id), in_item);

  return 1;
}

/* Define a new function in the hash table. */
void def_func(hashtbl in_hashtbl, funcp in_func, const char* id)
{
  stackitem* temp= malloc(sizeof(stackitem));

  temp->type= func;
  temp->content.ptr= in_func;

  mk_hashentry(in_hashtbl, temp, id);
}

/* Define a new symbol in the hash table. */
void def_sym(hashtbl in_hashtbl, const char* id)
{
  stackitem* temp= malloc(sizeof(stackitem));
  
  temp->type= symbol;
  mk_hashentry(in_hashtbl, temp, id);
}

/* Push a reference to an entry in the hash table onto the stack. */
int push_ref(stackitem** stack_head, hashtbl in_hash, const char* in_string)
{
  static void* handle= NULL;
  void* symbol;

  stackitem* new_item= malloc(sizeof(stackitem));
  new_item->content.ptr= *hash(in_hash, in_string);
  new_item->type= ref;

  if(new_item->content.ptr==NULL) { /* If hash entry empty */
    if(handle==NULL)            /* If no handle */
      handle= dlopen(NULL, RTLD_LAZY);    

    symbol= dlsym(handle, in_string); /* Get function pointer */
    if(dlerror()==NULL)         /* If existing function pointer */
      def_func(in_hash, symbol, in_string); /* Store function pointer */
    else
      def_sym(in_hash, in_string); /* Make symbol */
      
    new_item->content.ptr= *hash(in_hash, in_string); /* XXX */
    new_item->type= ref;
  }

  push(stack_head, new_item);
  return 1;
}

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

/* Discard the top element of the stack. */
extern void toss(stackitem** stack_head)
{
  stackitem* temp= *stack_head;

  if((*stack_head)==NULL) {
    printerr("Stack empty");
    return;
  }
  
  if((*stack_head)->type==string)
    free((*stack_head)->content.ptr);

  *stack_head= (*stack_head)->next;
  free(temp);
}

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

/* Prints the top element of the stack. */
void print_(stackitem** stack_head)
{
  if((*stack_head)==NULL) {
    printerr("Stack empty");
    return;
  }

  switch((*stack_head)->type) {
  case value:
    printf("%d", (*stack_head)->content.val);
    break;
  case string:
    printf("\"%s\"", (char*)(*stack_head)->content.ptr);
    break;
  case ref:
    printf("%s", ((stackitem*)(*stack_head)->content.ptr)->id);
    break;
  case symbol:
  default:
    printf("%p", (*stack_head)->content.ptr);
    break;
  }
}

/* Prints the top element of the stack and then discards it. */
extern void print(stackitem** stack_head)
{
  print_(stack_head);
  toss(stack_head);
}

/* Only to be called by function printstack. */
void print_st(stackitem* stack_head, long counter)
{ 
  if(stack_head->next != NULL)
    print_st(stack_head->next, counter+1);

  printf("%ld: ", counter);
  print_(&stack_head);
  nl();
}

/* Prints the stack. */
extern void printstack(stackitem** stack_head)
{
  if(*stack_head != NULL) {
    print_st(*stack_head, 1);
    nl();
  } else {
    printerr("Stack empty");
  }
}

/* If the top element is a reference, determine if it's a reference to a
   function, and if it is, toss the reference and execute the function. */
extern void eval(stackitem** stack_head)
{
  funcp in_func;

  if((*stack_head)==NULL || (*stack_head)->type!=ref) {
    printerr("Stack empty or not a reference");
    return;
  }

  if(((stackitem*)(*stack_head)->content.ptr)->type==func) {
    in_func= (funcp)((stackitem*)(*stack_head)->content.ptr)->content.ptr;
    toss(stack_head); 
    (*in_func)(stack_head);
    return;
  } else
    printerr("Not a function");
}

/* Make a list. */
extern void pack(stackitem** stack_head)
{
  void* delimiter;
  stackitem *iterator, *temp, *pack;

  if((*stack_head)==NULL) {
    printerr("Stack empty");
    return;
  }

  delimiter= (*stack_head)->content.ptr; /* Get delimiter */
  toss(stack_head);

  iterator= *stack_head;

  /* Search for first delimiter */
  while(iterator->next!=NULL && iterator->next->content.ptr!=delimiter)
    iterator= iterator->next;

  /* Extract list */
  temp= *stack_head;
  *stack_head= iterator->next;
  iterator->next= NULL;
  
  if(*stack_head!=NULL && (*stack_head)->content.ptr==delimiter)
    toss(stack_head);

  /* Push list */
  pack= malloc(sizeof(stackitem));
  pack->type= list;
  pack->content.ptr= temp;

  push(stack_head, pack);
}

/* Parse input. */
int stack_read(stackitem** stack_head, hashtbl in_hash, char* in_line) 
{
  char *temp, *rest;
  int itemp;
  size_t inlength= strlen(in_line)+1;
  int convert= 0;
  static int non_eval_flag= 0;

  temp= malloc(inlength);
  rest= malloc(inlength);

  do {
    /* If string */
    if((convert= sscanf(in_line, "\"%[^\"\n\r]\" %[^\n\r]", temp, rest))) {
      push_cstring(stack_head, temp);
      break;
    }
    /* If value */
    if((convert= sscanf(in_line, "%d %[^\n\r]", &itemp, rest))) {
      push_val(stack_head, itemp);
      break;
    }
    /* Escape ';' with '\' */
    if((convert= sscanf(in_line, "\\%c%[^\n\r]", temp, rest))) {
      temp[1]= '\0'; 
      push_ref(stack_head, in_hash, temp);
      break;
    } 
    /* If symbol */
    if((convert= sscanf(in_line, "%[^][ ;\n\r]%[^\n\r]", temp, rest))) {
        push_ref(stack_head, in_hash, temp);
        break;
    }
    /* If single char */
    if((convert= sscanf(in_line, "%c%[^\n\r]", temp, rest))) {
      if(*temp==';') {
        if(!non_eval_flag) {
          eval(stack_head);             /* Evaluate top element */
          break;
        }
        
        push_ref(stack_head, in_hash, ";");
        break;
      }

      if(*temp==']') {
        push_ref(stack_head, in_hash, "[");
        pack(stack_head);
        if(non_eval_flag!=0)
          non_eval_flag--;
        break;
      }

      if(*temp=='[') {
        push_ref(stack_head, in_hash, "[");
        non_eval_flag++;
        break;
      }
    }
  } while(0);


  free(temp);

  if(convert<2) {
    free(rest);
    return 0;
  }
   
  stack_read(stack_head, in_hash, rest);
  
  free(rest);
  return 1;
}

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

  /* Is top element a list? */
  if((*stack_head)==NULL || (*stack_head)->type!=list) {
    printerr("Stack empty or not a list");
    return;
  }

  /* The first list element is the new stack head */
  new_head= temp= (*stack_head)->content.ptr;
  toss(stack_head);

  /* Search the end of the list */
  while(temp->next!=NULL)
    temp= temp->next;

  /* Connect the the tail of the list with the old stack head */
  temp->next= *stack_head;
  *stack_head= new_head;        /* ...and voila! */
}

/* Swap the two top elements on the stack. */
extern void swap(stackitem** stack_head)
{
  stackitem* temp= (*stack_head);
  
  if((*stack_head)==NULL) {
    printerr("Stack empty");
    return;
  }

  if((*stack_head)->next==NULL)
    return;

  *stack_head= (*stack_head)->next;
  temp->next= (*stack_head)->next;
  (*stack_head)->next= temp;
} 

/* Compares two elements by reference. */
extern void eq(stackitem** stack_head)
{
  void *left, *right;
  int result;

  if((*stack_head)==NULL || (*stack_head)->next==NULL) {
    printerr("Not enough elements to compare");
    return;
  }

  left= (*stack_head)->content.ptr;
  swap(stack_head);
  right= (*stack_head)->content.ptr;
  result= (left==right);
  
  toss(stack_head); toss(stack_head);
  push_val(stack_head, (left==right));
}

/* Negates the top element on the stack. */
extern void not(stackitem** stack_head)
{
  int value;

  if((*stack_head)==NULL || (*stack_head)->type!=value) {
    printerr("Stack empty or element is not a value");
    return;
  }

  value= (*stack_head)->content.val;
  toss(stack_head);
  push_val(stack_head, !value);
}

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

/* Give a symbol some content. */
extern void def(stackitem** stack_head)
{
  stackitem *temp, *value;

  if(*stack_head==NULL || (*stack_head)->next==NULL 
     || (*stack_head)->type!=ref) {
    printerr("Define what?");
    return;
  }

  temp= (*stack_head)->content.ptr;
  value= (*stack_head)->next;
  temp->content= value->content;
  value->content.ptr=NULL;
  temp->type= value->type;

  toss(stack_head); toss(stack_head);
} 

/* Quit stack. */
extern void quit()
{
  exit(EXIT_SUCCESS);
}

int main()
{
  stackitem* s= NULL;
  hashtbl myhash;
  char in_string[100];

  init_hashtbl(myhash);

  printf("okidok\n ");

  while(fgets(in_string, 100, stdin) != NULL) {
    stack_read(&s, myhash, in_string);
    printf("okidok\n ");
  }

  exit(EXIT_SUCCESS);
}

/* Local Variables: */
/* compile-command:"make CFLAGS=\"-Wall -g -rdynamic -ldl\" stack" */
/* End: */
1	/* printf */
2	#include <stdio.h>
3	/* EXIT_SUCCESS */
4	#include <stdlib.h>
5	/* NULL */
6	#include <stddef.h>
7	/* dlopen, dlsym, dlerror */
8	#include <dlfcn.h>
9	/* assert */
10	#include <assert.h>
11
12	#define HASHTBLSIZE 65536
13
14	typedef struct stack_item
15	{
16	enum {
17	value, /* Integer */
18	string,
19	ref, /* Reference (to an element in the
20	hash table) */
21	func, /* Function pointer */
22	symbol,
23	list
24	} type; /* Type of stack element */
25
26	union {
27	void* ptr; /* Pointer to the content */
28	int val; /* ...or an integer */
29	} content; /* Stores a pointer or an integer */
30
31	char* id; /* Symbol name */
32	struct stack_item* next; /* Next element */
33	} stackitem;
34
35
36	typedef stackitem* hashtbl[HASHTBLSIZE]; /* Hash table declaration */
37	typedef void (funcp)(stackitem); / funcp is a pointer to a
38	void function (stackitem *) /
39
40	/* Initialize a newly created hash table. */
41	void init_hashtbl(hashtbl out_hash)
42	{
43	long i;
44
45	for(i= 0; i<HASHTBLSIZE; i++)
46	out_hash[i]= NULL;
47	}
48
49	/* Returns a pointer to an element in the hash table. */
50	stackitem** hash(hashtbl in_hashtbl, const char* in_string)
51	{
52	long i= 0;
53	unsigned long out_hash= 0;
54	char key= '\0';
55	stackitem** position;
56
57	while(1){ /* Hash in_string */
58	key= in_string[i++];
59	if(key=='\0')
60	break;
61	out_hash= out_hash*32+key;
62	}
63
64	out_hash= out_hash%HASHTBLSIZE;
65	position= &(in_hashtbl[out_hash]);
66
67	while(position != NULL){
68	if(position==NULL) / If empty */
69	return position;
70
71	if(strcmp(in_string, (position)->id)==0) / If match */
72	return position;
73
74	position= &((position)->next); / Try next */
75	}
76	return NULL; /* end of list reached without finding
77	an empty position */
78	}
79
80	/* Generic push function. */
81	int push(stackitem** stack_head, stackitem* in_item)
82	{
83	in_item->next= *stack_head;
84	*stack_head= in_item;
85	return 1;
86	}
87
88	/* Push a value on the stack. */
89	int push_val(stackitem** stack_head, int in_val)
90	{
91	stackitem* new_item= malloc(sizeof(stackitem));
92	assert(new_item != NULL);
93	new_item->content.val= in_val;
94	new_item->type= value;
95
96	push(stack_head, new_item);
97	return 1;
98	}
99
100	/* Copy a string onto the stack. */
101	int push_cstring(stackitem** stack_head, const char* in_string)
102	{
103	stackitem* new_item= malloc(sizeof(stackitem));
104	new_item->content.ptr= malloc(strlen(in_string)+1);
105	strcpy(new_item->content.ptr, in_string);
106	new_item->type= string;
107
108	push(stack_head, new_item);
109	return 1;
110	}
111
112	/* Create a new hash entry. */
113	int mk_hashentry(hashtbl in_hashtbl, stackitem* in_item, const char* id)
114	{
115	in_item->id= malloc(strlen(id)+1);
116
117	strcpy(in_item->id, id);
118	push(hash(in_hashtbl, id), in_item);
119
120	return 1;
121	}
122
123	/* Define a new function in the hash table. */
124	void def_func(hashtbl in_hashtbl, funcp in_func, const char* id)
125	{
126	stackitem* temp= malloc(sizeof(stackitem));
127
128	temp->type= func;
129	temp->content.ptr= in_func;
130
131	mk_hashentry(in_hashtbl, temp, id);
132	}
133
134	/* Define a new symbol in the hash table. */
135	void def_sym(hashtbl in_hashtbl, const char* id)
136	{
137	stackitem* temp= malloc(sizeof(stackitem));
138
139	temp->type= symbol;
140	mk_hashentry(in_hashtbl, temp, id);
141	}
142
143	/* Push a reference to an entry in the hash table onto the stack. */
144	int push_ref(stackitem** stack_head, hashtbl in_hash, const char* in_string)
145	{
146	static void* handle= NULL;
147	void* symbol;
148
149	stackitem* new_item= malloc(sizeof(stackitem));
150	new_item->content.ptr= *hash(in_hash, in_string);
151	new_item->type= ref;
152
153	if(new_item->content.ptr==NULL) { /* If hash entry empty */
154	if(handle==NULL) /* If no handle */
155	handle= dlopen(NULL, RTLD_LAZY);
156
157	symbol= dlsym(handle, in_string); /* Get function pointer */
158	if(dlerror()==NULL) /* If existing function pointer */
159	def_func(in_hash, symbol, in_string); /* Store function pointer */
160	else
161	def_sym(in_hash, in_string); /* Make symbol */
162
163	new_item->content.ptr= hash(in_hash, in_string); / XXX */
164	new_item->type= ref;
165	}
166
167	push(stack_head, new_item);
168	return 1;
169	}
170
171	void printerr(const char* in_string) {
172	fprintf(stderr, "Err: %s\n", in_string);
173	}
174
175	/* Discard the top element of the stack. */
176	extern void toss(stackitem** stack_head)
177	{
178	stackitem* temp= *stack_head;
179
180	if((*stack_head)==NULL) {
181	printerr("Stack empty");
182	return;
183	}
184
185	if((*stack_head)->type==string)
186	free((*stack_head)->content.ptr);
187
188	stack_head= (stack_head)->next;
189	free(temp);
190	}
191
192	/* Print newline. */
193	extern void nl()
194	{
195	printf("\n");
196	}
197
198	/* Prints the top element of the stack. */
199	void print_(stackitem** stack_head)
200	{
201	if((*stack_head)==NULL) {
202	printerr("Stack empty");
203	return;
204	}
205
206	switch((*stack_head)->type) {
207	case value:
208	printf("%d", (*stack_head)->content.val);
209	break;
210	case string:
211	printf("\"%s\"", (char)(stack_head)->content.ptr);
212	break;
213	case ref:
214	printf("%s", ((stackitem)(stack_head)->content.ptr)->id);
215	break;
216	case symbol:
217	default:
218	printf("%p", (*stack_head)->content.ptr);
219	break;
220	}
221	}
222
223	/* Prints the top element of the stack and then discards it. */
224	extern void print(stackitem** stack_head)
225	{
226	print_(stack_head);
227	toss(stack_head);
228	}
229
230	/* Only to be called by function printstack. */
231	void print_st(stackitem* stack_head, long counter)
232	{
233	if(stack_head->next != NULL)
234	print_st(stack_head->next, counter+1);
235
236	printf("%ld: ", counter);
237	print_(&stack_head);
238	nl();
239	}
240
241	/* Prints the stack. */
242	extern void printstack(stackitem** stack_head)
243	{
244	if(*stack_head != NULL) {
245	print_st(*stack_head, 1);
246	nl();
247	} else {
248	printerr("Stack empty");
249	}
250	}
251
252	/* If the top element is a reference, determine if it's a reference to a
253	function, and if it is, toss the reference and execute the function. */
254	extern void eval(stackitem** stack_head)
255	{
256	funcp in_func;
257
258	if((stack_head)==NULL \|\| (stack_head)->type!=ref) {
259	printerr("Stack empty or not a reference");
260	return;
261	}
262
263	if(((stackitem)(stack_head)->content.ptr)->type==func) {
264	in_func= (funcp)((stackitem)(stack_head)->content.ptr)->content.ptr;
265	toss(stack_head);
266	(*in_func)(stack_head);
267	return;
268	} else
269	printerr("Not a function");
270	}
271
272	/* Make a list. */
273	extern void pack(stackitem** stack_head)
274	{
275	void* delimiter;
276	stackitem iterator, temp, *pack;
277
278	if((*stack_head)==NULL) {
279	printerr("Stack empty");
280	return;
281	}
282
283	delimiter= (stack_head)->content.ptr; / Get delimiter */
284	toss(stack_head);
285
286	iterator= *stack_head;
287
288	/* Search for first delimiter */
289	while(iterator->next!=NULL && iterator->next->content.ptr!=delimiter)
290	iterator= iterator->next;
291
292	/* Extract list */
293	temp= *stack_head;
294	*stack_head= iterator->next;
295	iterator->next= NULL;
296
297	if(stack_head!=NULL && (stack_head)->content.ptr==delimiter)
298	toss(stack_head);
299
300	/* Push list */
301	pack= malloc(sizeof(stackitem));
302	pack->type= list;
303	pack->content.ptr= temp;
304
305	push(stack_head, pack);
306	}
307
308	/* Parse input. */
309	int stack_read(stackitem** stack_head, hashtbl in_hash, char* in_line)
310	{
311	char temp, rest;
312	int itemp;
313	size_t inlength= strlen(in_line)+1;
314	int convert= 0;
315	static int non_eval_flag= 0;
316
317	temp= malloc(inlength);
318	rest= malloc(inlength);
319
320	do {
321	/* If string */
322	if((convert= sscanf(in_line, "\"%[^\"\n\r]\" %[^\n\r]", temp, rest))) {
323	push_cstring(stack_head, temp);
324	break;
325	}
326	/* If value */
327	if((convert= sscanf(in_line, "%d %[^\n\r]", &itemp, rest))) {
328	push_val(stack_head, itemp);
329	break;
330	}
331	/* Escape ';' with '\' */
332	if((convert= sscanf(in_line, "\\%c%[^\n\r]", temp, rest))) {
333	temp[1]= '\0';
334	push_ref(stack_head, in_hash, temp);
335	break;
336	}
337	/* If symbol */
338	if((convert= sscanf(in_line, "%[^][ ;\n\r]%[^\n\r]", temp, rest))) {
339	push_ref(stack_head, in_hash, temp);
340	break;
341	}
342	/* If single char */
343	if((convert= sscanf(in_line, "%c%[^\n\r]", temp, rest))) {
344	if(*temp==';') {
345	if(!non_eval_flag) {
346	eval(stack_head); /* Evaluate top element */
347	break;
348	}
349
350	push_ref(stack_head, in_hash, ";");
351	break;
352	}
353
354	if(*temp==']') {
355	push_ref(stack_head, in_hash, "[");
356	pack(stack_head);
357	if(non_eval_flag!=0)
358	non_eval_flag--;
359	break;
360	}
361
362	if(*temp=='[') {
363	push_ref(stack_head, in_hash, "[");
364	non_eval_flag++;
365	break;
366	}
367	}
368	} while(0);
369
370
371	free(temp);
372
373	if(convert<2) {
374	free(rest);
375	return 0;
376	}
377
378	stack_read(stack_head, in_hash, rest);
379
380	free(rest);
381	return 1;
382	}
383
384	/* Relocate elements of the list on the stack. */
385	extern void expand(stackitem** stack_head)
386	{
387	stackitem temp, new_head;
388
389	/* Is top element a list? */
390	if((stack_head)==NULL \|\| (stack_head)->type!=list) {
391	printerr("Stack empty or not a list");
392	return;
393	}
394
395	/* The first list element is the new stack head */
396	new_head= temp= (*stack_head)->content.ptr;
397	toss(stack_head);
398
399	/* Search the end of the list */
400	while(temp->next!=NULL)
401	temp= temp->next;
402
403	/* Connect the the tail of the list with the old stack head */
404	temp->next= *stack_head;
405	stack_head= new_head; / ...and voila! */
406	}
407
408	/* Swap the two top elements on the stack. */
409	extern void swap(stackitem** stack_head)
410	{
411	stackitem* temp= (*stack_head);
412
413	if((*stack_head)==NULL) {
414	printerr("Stack empty");
415	return;
416	}
417
418	if((*stack_head)->next==NULL)
419	return;
420
421	stack_head= (stack_head)->next;
422	temp->next= (*stack_head)->next;
423	(*stack_head)->next= temp;
424	}
425
426	/* Compares two elements by reference. */
427	extern void eq(stackitem** stack_head)
428	{
429	void left, right;
430	int result;
431
432	if((stack_head)==NULL \|\| (stack_head)->next==NULL) {
433	printerr("Not enough elements to compare");
434	return;
435	}
436
437	left= (*stack_head)->content.ptr;
438	swap(stack_head);
439	right= (*stack_head)->content.ptr;
440	result= (left==right);
441
442	toss(stack_head); toss(stack_head);
443	push_val(stack_head, (left==right));
444	}
445
446	/* Negates the top element on the stack. */
447	extern void not(stackitem** stack_head)
448	{
449	int value;
450
451	if((stack_head)==NULL \|\| (stack_head)->type!=value) {
452	printerr("Stack empty or element is not a value");
453	return;
454	}
455
456	value= (*stack_head)->content.val;
457	toss(stack_head);
458	push_val(stack_head, !value);
459	}
460
461	/* Compares the two top elements on the stack and return 0 if they're the
462	same. */
463	extern void neq(stackitem** stack_head)
464	{
465	eq(stack_head);
466	not(stack_head);
467	}
468
469	/* Give a symbol some content. */
470	extern void def(stackitem** stack_head)
471	{
472	stackitem temp, value;
473
474	if(stack_head==NULL \|\| (stack_head)->next==NULL
475	\|\| (*stack_head)->type!=ref) {
476	printerr("Define what?");
477	return;
478	}
479
480	temp= (*stack_head)->content.ptr;
481	value= (*stack_head)->next;
482	temp->content= value->content;
483	value->content.ptr=NULL;
484	temp->type= value->type;
485
486	toss(stack_head); toss(stack_head);
487	}
488
489	/* Quit stack. */
490	extern void quit()
491	{
492	exit(EXIT_SUCCESS);
493	}
494
495	int main()
496	{
497	stackitem* s= NULL;
498	hashtbl myhash;
499	char in_string[100];
500
501	init_hashtbl(myhash);
502
503	printf("okidok\n ");
504
505	while(fgets(in_string, 100, stdin) != NULL) {
506	stack_read(&s, myhash, in_string);
507	printf("okidok\n ");
508	}
509
510	exit(EXIT_SUCCESS);
511	}
512
513	/* Local Variables: */
514	/* compile-command:"make CFLAGS=\"-Wall -g -rdynamic -ldl\" stack" */
515	/* End: */