Part 4 - Our Initial Parser

.gitignore

@@ -1,3 +1,5 @@
 program.rb
 lex.yy.c
 ruby
+parse.tab.c
+parse.tab.h

Makefile

@@ -1,10 +1,14 @@
+SRC=main.c parse.tab.c lex.yy.c
 all: ruby
 
-ruby: main.c lex.yy.c
-	cc -o ruby main.c lex.yy.c
+ruby: ${SRC}
+	cc -o ruby ${SRC}
 
 lex.yy.c: ruby.l
 	flex ruby.l
 
+parse.tab.c: parse.y
+	bison -d parse.y
+
 clean:
-	rm -rf ruby lex.yy.c
+	rm -rf ruby lex.yy.c parse.tab.c parse.tab.h

main.c

@@ -1,14 +1,14 @@
 #include <stdio.h>
 #include <stdlib.h>
+#include "parse.tab.h"
 
 extern FILE* yyin;
-extern int yylex(void);
 
 int main(int argc, char *argv[]) {
   if(argc > 1) {
     yyin = fopen(argv[1], "r");
   }
 
-  yylex();
+  yyparse();
   return EXIT_SUCCESS;
 }

parse.y

@@ -0,0 +1,19 @@
+%{
+  #include <stdio.h>
+  extern int yylex(void);
+  void yyerror(char const *s) { fprintf(stderr, "%s\n", s); }
+%}
+
+%token tNUMBER
+%token tPLUS
+%start program
+
+%%
+
+program: expressions
+
+expressions: expressions expression
+           | expression
+
+expression: tNUMBER
+          | expression tPLUS expression { printf("%d\n", $1 + $3); }

ruby.l

@@ -1,5 +1,6 @@
 %{
   #include <stdio.h>
+  #include "parse.tab.h"
   #define VTYPE(type, value) printf("%s(%s)\n", type, value)
   #define TYPE(type) printf("%s\n", type)
 %}
@@ -13,7 +14,7 @@ NUMBER [0-9](_[0-9]|[0-9])*
 \"([^"]|\\.)*\" { VTYPE("STRING", yytext); }
 \'([^']|\\.)*\' { VTYPE("STRING", yytext); }
 {NUMBER}(\.{NUMBER}|(\.{NUMBER})?[eE][+-]?{NUMBER}) { VTYPE("FLOAT", yytext); }
-{NUMBER} { VTYPE("NUMBER", yytext); }
+{NUMBER} { yylval = atoi(yytext); return tNUMBER; }
 [a-z_][a-zA-Z0-9_]* { VTYPE("ID", yytext); }
 [A-Z][a-zA-Z0-9_]* { VTYPE("CONSTANT", yytext); }
 "=" { TYPE("EQUAL"); }
@@ -22,7 +23,7 @@ NUMBER [0-9](_[0-9]|[0-9])*
 ">=" { TYPE("GTE"); }
 "<=" { TYPE("LTE"); }
 "!=" { TYPE("NEQUAL"); }
-"+" { TYPE("PLUS"); }
+"+" { return tPLUS; }
 "-" { TYPE("MINUS"); }
 "*" { TYPE("MULT"); }
 "/" { TYPE("DIV"); }