Coyoneda

Coyoneda.js

// helpers
var compose = function(f,g) {
  return function(x) {
    return f(g(x))
  }
}

var id = function(x) { return x }




// Define Coyoneda
var _Coyoneda = function(f, fa) {
  this.f = f;
  this.val = fa;
}

_Coyoneda.prototype.map = function(f) {
  return Coyoneda(compose(f, this.f), this.val)
}

_Coyoneda.prototype.lower = function() { return this.val.map(this.f); }


var Coyoneda = function(f, fa){ return new _Coyoneda(f, fa); }

Coyoneda.lift = function(x){ return Coyoneda(id, x); }



// Demo

var arr = [1,2,3]

var coyo_arr = Coyoneda.lift(arr);

var coyo_result = coyo_arr.map(function(x) { return x + 1 }).map(function(x) { return String(x) + '!' })

console.log("RESULT", coyo_result.lower());


//no map needed w/o lower()
coyo_result.val.forEach(function(x){
  console.log(coyo_result.f(x));
});

Coyoneda holds two values: a function that will build as we map and a functor-like container type.

The demo suggests we loop fuse the two maps and only iterate once.

A second forEach is thrown in to show that we don't need map after all, which is why Set can be "mapped" in yoneda, then run later by picking it apart.