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chriskrycho/need-HKTs.ts

Last active October 28, 2017 19:18
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Discovering the need/desire for higher-kinded types in TypeScript…
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need-HKTs.ts
import Maybe from './maybe';
import Result from './result';
// This isn't valid: you can't parameterize one type with another like I do here
// with M<T>, M<U> in TypeScript.
type Mappable<M, T, U> = {
map(this: M<T>, mapFn: (t: T) => U): M<U>;
};
export const map = <T, U>(mapFn: (t: T) => U, item: Mappable<typeof item, T, U>) => item.map(mapFn);
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