Jison arithmetic grammar

arithemetic.jison

%lex
%%
\s+                   /* skip ws */
[0-9]+                return 'NUMBER'
\+                    return 'ADD'
\-                    return 'SUB'
\*                    return 'MUL'
\/                    return 'DIV'
\(                    return 'LPAREN'
\)                    return 'RPAREN'
<<EOF>>               return 'EOF'
.                     return 'INVALID'
/lex

%start expressions

%%

expressions
	: expression EOF      { return $1; }
	;

expression
	: expression ADD term  { $$ = $1 + $3; }
	| expression SUB term  { $$ = $1 - $3; }
	| term               { $$ = $1; }
	;

term
	: term MUL factor  { $$ = $1 * $3; }
	| term DIV factor  { $$ = $1 / $3; }
	| factor           { $$ = $1; }
	;

factor
	: LPAREN expression RPAREN  { $$ = $2; }
	| NUMBER             { $$ = parseFloat(yytext); }
	;

%%