pipe.js

var assert = require('assert');

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


describe('pipe', function() {

  it('is a variadic function', function() {
    eq(typeof R.pipe, 'function');
    eq(R.pipe.length, 0);
  });

  it('performs left-to-right function composition', function() {
    //  f :: (String, Number?) -> ([Number] -> [Number])
    var f = R.pipe(parseInt, R.multiply, R.map);

    eq(f.length, 2);
    eq(f('10')([1, 2, 3]), [10, 20, 30]);
    eq(f('10', 2)([1, 2, 3]), [2, 4, 6]);
  });

  it('passes context to functions', function() {
    function x(val) {
      return this.x * val;
    }
    function y(val) {
      return this.y * val;
    }
    function z(val) {
      return this.z * val;
    }
    var context = {
      a: R.pipe(x, y, z),
      x: 4,
      y: 2,
      z: 1
    };
    eq(context.a(5), 40);
  });

  it('throws if given no arguments', function() {
    assert.throws(
      function() { R.pipe(); },
      function(err) {
        return err.constructor === Error &&
               err.message === 'pipe requires at least one argument';
      }
    );
  });

  it('can be applied to one argument', function() {
    var f = function(a, b, c) { return [a, b, c]; };
    var g = R.pipe(f);
    eq(g.length, 3);
    eq(g(1, 2, 3), [1, 2, 3]);
  });

});