flatmapFirst

import { flatmapFirst } from "https://github.gh-proxy.cn/raw.githubusercontent.com/baetheus/fun/main/either.ts";

Chain computations by applying a function that returns an Either to the Right value, but keep the original Right value if the function succeeds. This is useful for validation or side effects.

@example

import * as E from "./either.ts";

const validatePositive = (n: number) =>
  n > 0 ? E.right(n) : E.left("Number must be positive");

const result1 = E.flatmapFirst(validatePositive)(E.right(5));
// Right(5)

const result2 = E.flatmapFirst(validatePositive)(E.right(-3));
// Left("Number must be positive")

function flatmapFirst<A, I = never, J = never>(faui: (a: A) => Either<J, I>): (ta: Either<B, A>) => Either;

flatmapFirst<A, I = never, J = never>(faui: (a: A) => Either<J, I>): (ta: Either<B, A>) => Either

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§Type Parameters

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I = never

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J = never

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§Parameters

faui: (a: A) => Either<J, I>

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§Return Type

(ta: Either<B, A>) => Either

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