diff --git a/calc.leg b/calc.leg
new file mode 100644
index 0000000..1ca88c8
--- /dev/null
+++ b/calc.leg
@@ -0,0 +1,48 @@
+%{
+
+/* compile:	leg -o calc.c calc.leg
+ *		cc -o calc calc.c
+ *
+ * run:		echo "2+3" | ./calc
+ */
+
+#define YYSTYPE int
+YYSTYPE yylval = 0;
+
+%}
+
+start	=	e:exp				{ yylval = e }
+
+exp	=	- s:sum				{ $$ = s }
+
+sum	=	PLUS* l:prod
+		( PLUS+ r:prod			{ l += r }
+		| MINUS r:prod			{ l -= r }
+		)*				{ $$ = l }
+
+prod	=	l:neg
+		( MULTI		r:neg		{ l *= r }
+		| DIVIDE	r:neg		{ l /= r }
+		| MODULO	r:neg		{ l %= r }
+		)*				{ $$ = l }
+
+neg	=	MINUS n:neg			{ $$ = -n }
+		| n:NUMBER			{ $$ = n }
+
+-	=	[ \t]*
+NUMBER	=	< [0-9]+ >	-		{ $$ = atoi(yytext) }
+PLUS	=	'+'		-
+MINUS	=	'-'		-
+MULTI	=	'*'		-
+DIVIDE	=	'/'		-
+MODULO	=	'%'		-
+%%
+
+int main(int argc, char **argv)
+{
+	while (yyparse()) {
+		printf("%d\n", yylval);
+	}
+
+	return 0;
+}