ch1-04.l~

lex 与 yacc 源代码

%{
/*
 * Word recognizer with a symbol table.
 */

enum {
	LOOKUP = 0, /* default - looking rather than defining. */
	VERB,
	ADJ,
	ADV,
	NOUN,
	PREP,
	PRON,
	CONJ
};

int state; 

int add_word(int type, char *word);
int lookup_word(char *word);
%}
%%
\n	{ state = LOOKUP; }	/* end of line, return to default state */

^verb	{ state = VERB; }
^adj	{ state = ADJ; }
^adv	{ state = ADV; }
^noun	{ state = NOUN; }
^prep	{ state = PREP; }
^pron	{ state = PRON; }
^conj	{ state = CONJ; }

[a-zA-Z]+  {
		/* a normal word, define it or look it up */
	     if(state != LOOKUP) {
	        /* define the current word */
	     	add_word(state, yytext);
	     } else {
		switch(lookup_word(yytext)) {
		case VERB: printf("%s: verb\n", yytext); break;
		case ADJ: printf("%s: adjective\n", yytext); break;
		case ADV: printf("%s: adverb\n", yytext); break;
		case NOUN: printf("%s: noun\n", yytext); break;
		case PREP: printf("%s: preposition\n", yytext); break;
		case PRON: printf("%s: pronoun\n", yytext); break;
		case CONJ: printf("%s: conjunction\n", yytext); break;
		default:
			printf("%s:  don't recognize\n", yytext);
			break;
		}
            }
          }

.	/* ignore anything else */ ;

%%
main()
{
	yylex();
}

/* define a linked list of words and types */
struct word {
	char *word_name;
	int word_type;
	struct word *next;
};

struct word *word_list; /* first element in word list */

extern void *malloc();

int
add_word(int type, char *word)
{
	struct word *wp;	

	if(lookup_word(word) != LOOKUP) {
		printf("!!! warning: word %s already defined \n", word);
		return 0;
	}
	
	/* word not there, allocate a new entry and link it on the list */

	wp = (struct word *) malloc(sizeof(struct word));

	wp->next = word_list;

	/* have to copy the word itself as well */
	
	wp->word_name = (char *) malloc(strlen(word)+1);
	strcpy(wp->word_name, word);
	wp->word_type = type;
	word_list = wp;
	return 1;	/* it worked */
}

int
lookup_word(char *word)
{
	struct word *wp = word_list;

	/* search down the list looking for the word */
	for(; wp; wp = wp->next) {
		if(strcmp(wp->word_name, word) == 0)
			return wp->word_type;
	}

	return LOOKUP;	/* not found */
}