ch1-05.l

%{
/*
 * We now build a lexical analyzer to be used by a higher-level parser.
 */

#include "ch1-05.h"
#include "ch1-05.tab.h"  /* token codes from the parser */

#define LOOKUP 0 /* default - not a defined word type. */

int state;

int lookup_word(char *word);
int add_word(int type, char *word);
%}

%%

\n { state = LOOKUP; }

\.\n {
    state = LOOKUP;
    return 0; /* end of sentence */
  }

^verb  { state = VERB; }
^adj   { state = ADJECTIVE; }
^adv   { state = ADVERB; }
^noun  { state = NOUN; }
^prep  { state = PREPOSITION; }
^pron  { state = PRONOUN; }
^conj  { state = CONJUNCTION; }

[a-zA-Z]+ { 
    if(state != LOOKUP) {
      add_word(state, yytext);
    } else {
      switch(lookup_word(yytext)) {
      case VERB: return(VERB);
      case ADJECTIVE: return(ADJECTIVE);
      case ADVERB: return(ADVERB);
      case NOUN: return(NOUN);
      case PREPOSITION: return(PREPOSITION);
      case PRONOUN: return(PRONOUN);
      case CONJUNCTION: return(CONJUNCTION);
      default:
        printf("%s:  don't recognize\n", yytext);
        /* don't return, just ignore it */
      }
    }
  }

. {;}

%%
/* 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 */

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 */
}

int yywrap()
{
  return 1;
}