Merge pull request #14 from mame/add-calc-sample

Add a sample of calculator

sample/calc.y

@@ -0,0 +1,97 @@
+/*
+ * How to build and run:
+ *
+ * $ lrama -d calc.y -o calc.c && gcc -Wall calc.c -o calc && ./calc
+ * 1
+ * => 1
+ * 1+2*3
+ * => 7
+ * (1+2)*3
+ * => 9
+ *
+ */
+
+%{
+#include <stdio.h>
+#include <stdlib.h>
+#include <ctype.h>
+
+#include "calc.h"
+
+static int yylex(YYSTYPE *val, YYLTYPE *loc);
+static int yyerror(YYLTYPE *loc, const char *str);
+%}
+
+%union {
+    int val;
+}
+%token LF
+%token <val> NUM
+%type <val> expr
+%left '+' '-'
+%left '*' '/'
+
+%%
+
+list : /* empty */
+     | list LF
+     | list expr LF { printf("=> %d\n", $2); }
+     ;
+expr : NUM
+     | expr '+' expr { $$ = $1 + $3; }
+     | expr '-' expr { $$ = $1 - $3; }
+     | expr '*' expr { $$ = $1 * $3; }
+     | expr '/' expr { $$ = $1 / $3; }
+     | '(' expr ')'  { $$ = $2; }
+     ;
+
+%%
+
+static int yylex(YYSTYPE *yylval, YYLTYPE *loc) {
+    int c = getchar();
+    int val;
+
+    switch (c) {
+    case ' ': case '\t':
+        return yylex(yylval, loc);
+
+    case '0': case '1': case '2': case '3': case '4':
+    case '5': case '6': case '7': case '8': case '9':
+        val = c - '0';
+        while (1) {
+            c = getchar();
+            if (isdigit(c)) {
+                val = val * 10 + (c - '0');
+            }
+            else {
+                ungetc(c, stdin);
+                break;
+            }
+        }
+        yylval->val = val;
+        return NUM;
+
+    case '\n':
+        return LF;
+
+    case '+': case '-': case '*': case '/': case '(': case ')':
+        return c;
+
+    case EOF:
+        exit(0);
+
+    default:
+        fprintf(stderr, "unknown character: %c\n", c);
+        exit(1);
+    }
+}
+
+static int yyerror(YYLTYPE *loc, const char *str) {
+    fprintf(stderr, "parse error: %s\n", str);
+    return 0;
+}
+
+int main() {
+    yyparse();
+    return 0;
+}