functorsExercise.js

var P = require('pointfree-fantasy');
var R = require('ramda');
var F = require('folktale');

var map = R.map;
var compose = P.compose;
//var Maybe = require('./maybe').Maybe;
var Maybe = require('data.maybe');
var Identity = P.I;
var capitalize = require('ramda').toUpper;

// Exercise 1
// ==========
// Use _.add(x,y) and map(f,x) to make a function that increments a value inside a functor
console.log("--------Start exercise 1--------");

var ex1 = map(R.add(1));

assertDeepEqual(Identity(3), ex1(Identity(2)));
console.log("exercise 1...ok!");

// Exercise 2
// ==========
// Use _.head to get the first element of the list
var xs = Identity(['do', 'ray', 'me', 'fa', 'so', 'la', 'ti', 'do']);
console.log("--------Start exercise 2--------");

var ex2 = R.map(R.head);

assertDeepEqual(Identity('do'), ex2(xs));
console.log("exercise 2...ok!");

// Exercise 3
// ==========
// Use safeGet and _.head to find the first initial of the user
var safeGet = R.curry(function(x,o){ return Maybe(o[x]) });
var user = {id: 2, name: "Albert"};
console.log("--------Start exercise 3--------");

var ex3 = compose(map(R.head), safeGet('name'));

assertDeepEqual(Maybe('A'), ex3(user));
console.log("exercise 3...ok!");

// Exercise 4
// ==========
// Use Maybe to rewrite ex4 without an if statement
console.log("--------Start exercise 4--------");

//var ex4 = function(n) {
//	if(n){
//		return parseInt(n);
//	}
//}

var pi = R.curry(function (x) {
	return parseInt(x, 10);
});

//var ex4 = R.compose(Maybe, pi);
var ex4 = R.compose(map(pi), Maybe);

assertDeepEqual(Maybe(4), ex4("4"));
console.log("exercise 4...ok!");














// TEST HELPERS
// =====================
function inspectIt(x){
	return (x.inspect && x.inspect()) || (x.toString && x.toString()) || x.valueOf(); //hacky for teachy.
}

function assertEqual(x,y){
	if(x !== y){ throw("expected "+x+" to equal "+y); }
}
function assertDeepEqual(x,y){
	if(x.val !== y.val) throw("expected "+inspectIt(x)+" to equal "+inspectIt(y));
}