Proxy JS

proxy.js

// `proxy` is a function to allow for point-free recursion in JavaScrpipt 
// it takes in a function name as a string, and returns a proxy function to the original function

// examples

// explicit proxy - save proxy after declaration
// var length = ifElse(isEmpty, always(0), compose(inc, proxy('length'), tail));
// proxy('length', length);

// use short had proxy chaining
// var length = ifElse(isEmpty, always(0), compose(inc, proxy('length'), tail)).proxy('length');

// wrap declaration with proxy
// var length = proxy('length', ifElse(isEmpty, always(0), compose(inc, proxy('length'), tail)));

// invoke the proxy directly
// proxy('length', ifElse(isEmpty, always(0), compose(inc, proxy('length'), tail)));
// proxy('length')([1, 2, 3, 4])

var R = require('ramda');

var dropArgs = function(n) {
  return R.compose(R.drop(2), getArgs);
};

var getArgs = function() {
  return toArray(arguments);
};

var both = function(v1, v2) {
  return v1 && v2;
};

var toArray = function(o) {
  return Array.prototype.slice.call(o);
};

var proxies = {};

// Object -> String -> Function -> Function
var setProxy = R.partial(function(proxies, name, fn) {
  proxies[name] = fn;
  return fn;
}, proxies);

// Object -> String -> Function
var getProxy = R.partial(function(proxies, name) {
  return R.partial(useProxy, proxies, name);
}, proxies);

// Object -> String -> IO
var throwProxyError = function(proxies, name) {
  throw new Error('No established proxy for function: ' + name);
};

// Object -> String -> * -> *
var useProxy = R.ifElse(
  R.propOf, R.converge(R.apply, R.propOf, dropArgs(2)), throwProxyError
);

// String, (Function) -> Function
var proxy = R.ifElse(both, setProxy, getProxy);

Function.prototype.proxy = function(name) {
  return proxy(name, this);
};

module.exports = proxy;