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grammar.y

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+//A01781041
+%{
+#include <stdio.h>
+#include <stdlib.h>
+
+// Declare yyin and yylineno if they're not already defined by Flex
+extern FILE *yyin;
+extern int yylineno;
+
+void yyerror(const char *s) {
+  fprintf(stderr, "Error: %s at line %d\n", s, yylineno);
+  exit(EXIT_FAILURE);
+}
+
+int yylex(void);
+%}
+
+%token ARTICLE BOY GIRL FLOWER TOUCHES LIKES SEES WITH
+
+%%
+
+SENTENCE: NOUN_PHRASE VERB_PHRASE
+        ;
+
+NOUN_PHRASE: ARTICLE NOUN
+           | ARTICLE NOUN PREP_PHRASE
+           ;
+
+NOUN: BOY
+    | GIRL
+    | FLOWER
+    ;
+
+VERB_PHRASE: VERB
+           | VERB NOUN_PHRASE
+           ;
+
+VERB: TOUCHES
+    | LIKES
+    | SEES
+    ;
+
+PREP_PHRASE: WITH NOUN_PHRASE
+           ;
+
+%%
+
+int main(int argc, char *argv[]) {
+  if (argc != 2) {
+    fprintf(stderr, "Usage: %s <filename>\n", argv[0]);
+    exit(EXIT_FAILURE);
+  }
+
+  FILE *file = fopen(argv[1], "r");
+  if (!file) {
+    perror(argv[1]);
+    exit(EXIT_FAILURE);
+  }
+
+  yyin = file;
+
+  // Parse through the input until there is no more:
+  do {
+    yyparse();
+  } while (!feof(yyin));
+
+  fclose(file);
+  return 0;
+}

tokens.l

@@ -0,0 +1,24 @@
+%{
+#include "grammar.tab.h"
+%}
+
+%option yylineno
+
+%%
+
+[aA]                     { return ARTICLE; }
+boy                      { return BOY; }
+girl                     { return GIRL; }
+flower                   { return FLOWER; }
+touches                  { return TOUCHES; }
+likes                    { return LIKES; }
+sees                     { return SEES; }
+with                     { return WITH; }
+[ \t\n]+                 ; /* Ignore whitespaces and newlines */
+.                        ; /* Ignore other characters */
+
+%%
+
+int yywrap(void) {
+  return 1;
+}