Fun with a Lazy type and pairs
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// Pair helpers | |
// Map the first element of a pair | |
const first = <A, B, C> (f: A => B, [a, c]: [A, C]): [B, C] => | |
[f(a), c] | |
// Map the second element of a pair | |
const second = <A, B, C> (f: B => C, [a, b]: [A, B]): [A, C] => | |
[a, f(b)] | |
// Lazy type | |
type Lazy<A> = () => A | |
const lazy = <A> (a: A): Lazy<A> => | |
() => a | |
const force = <A> (la: Lazy<A>): A => | |
la() | |
const mapLazy = <A, B> (f: A => B, la: Lazy<A>): Lazy<B> => | |
() => f(force(la)) | |
const firstLazy = <A, B, C> (f: A => B, lp: Lazy<[A, C]>): Lazy<[B, C]> => | |
() => first(f, force(lp)) | |
const secondLazy = <A, B, C> (f: B => C, lp: Lazy<[A, B]>): Lazy<[A, C]> => | |
() => second(f, force(lp)) |
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