type-checking-horror.js

(function() {
  var $f;
  
  $f = function $f() {
    var types = Array.prototype.slice.call(arguments);
    var returnType;
    
    function defineReturn(val) {
      returnType = val;
      return defineFn;
    };
    
    function defineFn(fn) {
      var wrapper = function() {
        checkPairs(types, arguments);
        var returnValue = fn.apply(arguments);
        if (returnType && !typeCheck(returnValue, returnType)) {
          throw new Error("The return type of this function is incorrect.");
        }
        return returnValue;
      }
      wrapper.paramTypes = types;
      wrapper.returnType = returnType;
      wrapper.unwrapped = fn;
      return wrapper;
    };
    
    return defineReturn;
  };
  
  function checkPairs(types, values) {
    var l = types.length;
    for (var i = 0; i < l; i++) {
      if (!typeCheck(values[i], types[i])) {
        throw new Error("Expected type not received.");
      }
    }
  };

  function typeCheck(obj, type) {
    if (type === undefined || type === null) {
      return obj === type;
    }
    else {
      return obj.constructor === type;
    }
  };
  
  this.$f = $f;

})();