CodeMirror

 /* description: Parses end executes mathematical expressions. */ /* lexical grammar */ %lex %% \s+ /* skip whitespace */ [0-9]+("."[0-9]+)?\b return 'NUMBER'; "*" return '*'; "/" return '/'; "-" return '-'; "+" return '+'; "^" return '^';

                    "(" return '('; ")" return ')'; "PI" return 'PI'; "E" return 'E'; <<EOF>> return 'EOF'; /lex /* operator associations and precedence */ %left '+' '-' %left '*' '/' %left '^' %left UMINUS %start expressions %% /* language

                    grammar */ expressions : e EOF {print($1); return $1;} ; e : e '+' e {$$ = $1+$3;} | e '-' e {$$ = $1-$3;} | e '*' e {$$ = $1*$3;} | e '/' e {$$ = $1/$3;} | e '^' e {$$ = Math.pow($1, $3);} | '-' e %prec UMINUS {$$ = -$2;} | '(' e

                    ')' {$$ = $2;} | NUMBER {$$ = Number(yytext);} | E {$$ = Math.E;} | PI {$$ = Math.PI;} ;