tack-on

Some neato functions inspired by the new bind operator and functional programming.

tack

Attach a function to a thing, without hanging it directly. Great to add functionality that should have been there from the start, without the risk of mutating global objects.

tack(func, injectPosition = 0, actionFunc?)

What?

import mapValues from 'lodash';
import { tack } from 'tack-on';
 
const map = tack(mapValues);
let succ = n => n + 1;
 
expect({ a: 1, b: 2 }::map(succ)).to.deep.equal({ a: 2, b: 3 });

Tacked functions assume composing behavior when bound to functions.

const succ = tack(n => n + 1);
const pred = tack(n => n - 1);
 
expect(succ::pred::succ::succ(0)).to.equal(2);

The position this is inserted into can be specified.

const toTriple = tack((a, b, c) => [a, b, c], 1);
 
expect('middle'::toTriple('start', 'end')).to.equal(['start', 'middle', 'end']);

A custom action function can be provided that will change the defaults for when to tack, when to compose and when to do call the original function.

const f = tack(
  func => func(2),
  0,
  t => t !== undefined ? 'tack' : 'nothing'
);
 
// f will tack to functions instead of composing with them.
 
expect(succ::f()).to.equal(3);

the action function can return "tack", "compose", or "nothing".

When doing the "nothing" action, the binding is passed through to the tacked function.

compose

Make functions composable with the bind operator. compose assumes functions that take only one argument.

What?

import { compose } from 'tack-on';
 
succ = compose(succ);
const pred = compose(n => n - 1);
 
expect(succ::pred::succ::succ::succ::pred(1)).to.equal(3)
 
const addThreeMorphism = succ::succ::succ;
 
expect(addThreeMorphism(3)).to.equal(6);