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@Kvest
Created June 4, 2019 16:11
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/**
* Copyright (C) 2018 Fernando Cejas Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
* Represents a value of one of two possible types (a disjoint union).
* Instances of [Either] are either an instance of [Left] or [Right].
* FP Convention dictates that [Left] is used for "failure"
* and [Right] is used for "success".
*
* @see Left
* @see Right
*/
sealed class Either<out L, out R> {
/** * Represents the left side of [Either] class which by convention is a "Failure". */
data class Left<out L>(val a: L) : Either<L, Nothing>()
/** * Represents the right side of [Either] class which by convention is a "Success". */
data class Right<out R>(val b: R) : Either<Nothing, R>()
val isRight get() = this is Right<R>
val isLeft get() = this is Left<L>
fun <L> left(a: L) = Either.Left(a)
fun <R> right(b: R) = Either.Right(b)
fun either(fnL: (L) -> Any, fnR: (R) -> Any): Any =
when (this) {
is Left -> fnL(a)
is Right -> fnR(b)
}
}
// Credits to Alex Hart -> https://proandroiddev.com/kotlins-nothing-type-946de7d464fb
// Composes 2 functions
fun <A, B, C> ((A) -> B).c(f: (B) -> C): (A) -> C = {
f(this(it))
}
fun <T, L, R> Either<L, R>.flatMap(fn: (R) -> Either<L, T>): Either<L, T> =
when (this) {
is Either.Left -> Either.Left(a)
is Either.Right -> fn(b)
}
fun <T, L, R> Either<L, R>.map(fn: (R) -> (T)): Either<L, T> = this.flatMap(fn.c(::right))
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