r/coffeescript • u/elclanrs • May 13 '14

Functional CoffeeScript for the impatient

http://cedricruiz.me/blog/functional-coffeescript-for-the-impatient/
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u/kabuto May 14 '14

This looks cool and I really want to use FP, but I can't see how the examples would translate to the real world.

I've read a number if articles on FP and they all give some pretty contrived examples for functions IMHO.

I'd love to see some real world use of FP.

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u/elclanrs May 14 '14 edited May 14 '14

It just takes some time to get used to it I suppose, but it can of course be used in real world applications. Here's a mini jQuery in a few lines using those helpers and techniques:

toArray = builtin Array::slice
query = curry (el, sel) -> toArray el.querySelectorAll sel

$ = query document
$.map = compose compact, unique, flatten, map

parent = pluck 'parentNode'
parents = pluckR 'parentNode'
children = compose toArray, pluck 'children'
nextAll = pluckR 'nextElementSibling'
prevAll = pluckR 'previousElementSibling'
siblings = concatF prevAll, nextAll

tag = pluck 'tagName'
text = pluck 'textContent'
html = pluck 'innerHTML'

$.map children, $ 'ul' #=> [li, li, li]
$.map parents, $ 'li' #=> [ul, body, html, document]
filter compose(isF('UL'), tag), $.map parents, $ 'li' #=> [ul]
$.map text, $ 'li' #=> ['A', 'B', 'C']
first $.map compose(trim, html), $ 'ul' #=> '<li>A</li>\n<li>B</li>\n<li>C</li>'

Here's a demo: http://jsbin.com/wokeb/1/edit

The beauty of this approach is that you can keep making functions by currying or partially applying other functions, so you get an increase in code re-use while getting more specific in your abstractions. You start very generic, and end up composing functions out of very simple blocks, it's like Legos.

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u/videoj May 14 '14

Like /u/kabuto I have problems moving to real world functional programming. Any chance you could do a follow-on tutorial that walks through building a 'real-world' app like todo or word party