%{/* * A lexer for the basic grammar to use for recognizing english sentences. */#include <stdio.h>%}%token NOUN PRONOUN VERB ADVERB ADJECTIVE PREPOSITION CONJUNCTION%%sentence: subject VERB object	{ printf("Sentence is valid.\n"); }	;subject:	NOUN	|	PRONOUN	;object:		NOUN	;%%extern FILE *yyin;main(){	while(!feof(yyin)) {		yyparse();	}}yyerror(s)char *s;{    fprintf(stderr, "%s\n", s);}