Last active
April 29, 2016 15:26
-
-
Save anler/3b42b313a372fcb1a60acb1cd61a78db to your computer and use it in GitHub Desktop.
Purely functional implementation of streams in JavaScript borrowed from SICP
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
const EMPTY = null; | |
console.clear(); | |
var naturals$ = Naturals() | |
var firstFive$ = take(5, naturals$) | |
applyEach( | |
n => console.log(n), | |
firstFive$ | |
) | |
// 1 2 3 4 5 | |
function Naturals(startAt=1) { | |
return unshift( | |
startAt, | |
defer(Naturals, startAt + 1) | |
) | |
} | |
function take(n, s) { | |
if (isEmpty(s) || | |
n < 1) return empty() | |
return unshift( | |
head(s), | |
defer(take, n - 1, tail(s)) | |
) | |
} | |
function defer(f, ...args) { | |
return function() { | |
return f.apply(null, args) | |
} | |
} | |
function applyEach(f, s) { | |
if (isEmpty(s)) return empty() | |
f( head(s) ) // side-effect | |
return applyEach( | |
f, | |
tail(s) | |
) | |
} | |
function head(s) { | |
return s('head') | |
} | |
function tail(s) { | |
return demand( s('tail') ) | |
} | |
function demand(f) { | |
return f(); | |
} | |
function unshift(head, tail) { | |
return function get(ref) { | |
switch (ref) { | |
case 'head': return head; | |
case 'tail': return tail; | |
} | |
} | |
} | |
function empty() { | |
return EMPTY; | |
} | |
function isEmpty(s) { | |
return s === EMPTY; | |
} |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment