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zaetrik/monads-flatmap-chain.ts

Last active May 12, 2020 08:38
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Monads: flatMap & chain
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monads-flatmap-chain.ts
interface Monad<M> extends Applicative<M> {
flatMap: <A, B>(f: (a: A) => M<B>) => ((ma: M<A>) => M<B>);
}
// An implementation could look like this
const OptionMonad = {
...OptionApplicative,
flatMap: (f) => (ma) => (isNone(ma) ? none : f(ma.value)),
}
// In fp-ts a variant of flatMap is used => chain
// chain is almsot like flatMap but the arguments are rearranged
interface Monad<M> extends Applicative<M> {
chain: <A, B>(ma: M<A>, f: (a: A) => M<B>) => M<B>;
}
// An implementation with chain could look like this
const OptionMonad = {
...OptionApplicative,
chain: (ma, f) => (isNone(ma) ? none : f(ma.value)),
}
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