Jison

Calculator demo

This demo parses mathematical expressions and returns the answer, keeping the correct order of operations.

Enter an expression to evaluate, such as PI*4^2 + 5:

equals

The grammar

This Jison grammar was used to create the parser/evaluator:

/* description: Parses and executes mathematical expressions. */

/* lexical grammar */
%lex
%%

\s+                   /* skip whitespace */
[0-9]+("."[0-9]+)?\b  return 'NUMBER';
"*"                   return '*';
"/"                   return '/';
"-"                   return '-';
"+"                   return '+';
"^"                   return '^';
"!"                   return '!';
"%"                   return '%';
"("                   return '(';
")"                   return ')';
"PI"                  return 'PI';
"E"                   return 'E';
<<EOF>>               return 'EOF';
.                     return 'INVALID';

/lex

/* operator associations and precedence */

%left '+' '-'
%left '*' '/'
%left '^'
%right '!'
%right '%'
%left UMINUS
%token INVALID

%start expressions

%% /* language grammar */

expressions
    : e EOF
        { typeof console !== 'undefined' ? console.log($1) : print($1);
          return $1; }
    ;

e
    : e '+' e
        {$$ = $1 + $3;}
    | e '-' e
        {$$ = $1 - $3;}
    | e '*' e
        {$$ = $1 * $3;}
    | e '/' e
        {$$ = $1 / $3;}
    | e '^' e
        {$$ = Math.pow($1, $3);}
    | e '!'
        {{
          $$ = (function fact(n) { return n == 0 ? 1 : fact(n - 1) * n; })($1);
        }}
    | e '%'
        {$$ = $1 / 100;}
    | '-' e %prec UMINUS
        {$$ = -$2;}
    | '(' e ')'
        {$$ = $2;}
    | NUMBER
        {$$ = Number(yytext);}
    | E
        {$$ = Math.E;}
    | PI
        {$$ = Math.PI;}
    ;