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export interface IEither<E, T> {
ok?: T;
err?: E;
mapBoth: <Ee, Tt>(
errBranch: (e: E) => Ee,
okBranch: (o: T) => Tt,
) => IEither<Ee, Tt>;
mapRight: <Tt>(mapper: (t: T) => Tt) => Either<E, Tt>;
mapLeft: <Ee>(mapper: (e: E) => Ee) => Either<Ee, T>;
flatMap: <Ee extends E, Tt>(
mapper: (e: T) => Either<Ee, Tt>,
) => Either<Ee, Tt>;
}
export class Either<E, T> implements IEither<E, T> {
private constructor(readonly err?: E, readonly ok?: T) {}
public mapBoth<Ee, Tt>(
errBranch: (e: E) => Ee,
okBranch: (t: T) => Tt,
): Either<Ee, Tt> {
if (this.err) return Either.left(errBranch(this.err));
return Either.right(okBranch(this.ok!));
}
public flatMap<Ee extends E, Tt>(mapper: (t: T) => Either<Ee, Tt>) {
if (this.ok) return mapper(this.ok);
return this;
}
public mapRight<Tt>(mapper: (t: T) => Tt): Either<E, Tt> {
if (this.ok) return Either.right(mapper(this.ok));
return Either.left(this.err!);
}
public mapLeft<Ee>(mapper: (e: E) => Ee): Either<Ee, T> {
if (this.err) return Either.left(mapper(this.err));
return Either.right(this.ok!);
}
static left<E, T>(e: E) {
return new Either<E, T>(e);
}
static right<E, T>(t: T) {
return new Either<E, T>(undefined, t);
}
}
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