ivenmarquardt
/ lazy-evaluation.js
Last active
May 18, 2018 20:37
Lazy evaluation, lazy getters, eta reduction, function composition, implicit thunks through deferred type
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| // Lazy Getters | |
| /* What enables Tail Recursion Modulo Cons in Javascript is a thunk in Weak Head Normal Form. | |
| An expression in weak head normal form has been evaluated to the outermost data constructor, | |
| but contains sub-expressions that may not have been fully evaluated. In Javascript only thunks | |
| can prevent sub-expressions from being immediately evaluated. */ | |
| const cons = (head, tail) => ({head, tail}); |
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| let cache = new Map(); | |
| let pending = new Map(); | |
| function fetchTextSync(url) { | |
| if (cache.has(url)) { | |
| return cache.get(url); | |
| } | |
| if (pending.has(url)) { | |
| throw pending.get(url); | |
| } |