string to function

string.to_f.js

String.prototype.to_f = function() {
  var method = this;
  var arity = method.match(/arity:(\d+)/);
  var argument_count = -1;
  if (arity) {
    arity = arity[1];
    argument_count = 1 + arity;
  }
  
  method = method.replace(/\s*arity:\d+/, '');
  var passed_args = Array().slice.call(arguments);
  return function() {
    var args = Array().slice.call(arguments, 0, argument_count);
    var obj = args.shift();
    var fn = obj[method];
    if (fn) {
      if (typeof fn == 'function') {
        return fn.apply(obj, passed_args);
      } else {
        return fn;
      }
    } else {
      var operands = [obj];
      for (var i=0; i < arity; i++) {
        operands.push(args[i]);
      };
      operands = operands.concat(passed_args);
      if (typeof obj == 'string') {
        var quote = obj.match(/"/) ? "'" : '"';
        for (var i=0; i < operands.length; i++) {
          operands[i] = quote + operands[i] + quote;
        };
      }
      var expression = operands.join(' ' + method + ' ');
      return eval(expression);
    }
  };
};


var u = require('underscore');

> 
> u([4, 5, 6]).map("+ arity:0".to_f(2));
[ 6, 7, 8 ]
> u(['4-4', '5-5', '6-6']).reduce("+ arity:1".to_f(''));
'4-45-56-6'
> u([4, 5, 6]).reduce("+ arity:1".to_f(0));
15
> u([4, 5, 6]).map(">> arity:0".to_f(1));
[ 2, 2, 3 ]
> u([4, 5, 6]).map("<< arity:0".to_f(1));
[ 8, 10, 12 ]
> u([4, 5, 6]).reduce("* arity:1".to_f(1));
120
> u([1, 2, 3]).map("+ arity:0".to_f(2));
[ 3, 4, 5 ]
> u(['abc', 'defg', 'hijkl']).map('toUpperCase'.to_f());
[ 'ABC', 'DEFG', 'HIJKL' ]
>