either.js

const { Nothing, Just } = require('sanctuary');

var R = require('../source/index.js');
var eq = require('./shared/eq.js');


describe('either', function() {
  it('combines two boolean-returning functions into one', function() {
    var even = function(x) {return x % 2 === 0;};
    var gt10 = function(x) {return x > 10;};
    var f = R.either(even, gt10);
    eq(f(8), true);
    eq(f(13), true);
    eq(f(7), false);
  });

  it('accepts functions that take multiple parameters', function() {
    var between = function(a, b, c) {return a < b && b < c;};
    var total20 = function(a, b, c) {return a + b + c === 20;};
    var f = R.either(between, total20);
    eq(f(4, 5, 8), true);
    eq(f(12, 2, 6), true);
    eq(f(7, 5, 1), false);
  });

  it('does not evaluate the second expression if the first one is true', function() {
    var T = function() { return true; };
    var Z = function() { effect = 'Z got evaluated'; };
    var effect = 'not evaluated';
    R.either(T, Z)();
    eq(effect, 'not evaluated');
  });

  it('accepts fantasy-land applicative functors', function() {
    eq(R.either(Just(true), Just(true)), Just(true));
    eq(R.either(Just(true), Just(false)), Just(true));
    eq(R.either(Just(false), Just(false)), Just(false));
    eq(R.either(Just(true), Nothing), Nothing);
    eq(R.either(Nothing, Just(false)), Nothing);
    eq(R.either(Nothing, Nothing), Nothing);
  });
});