Add flatmap and map to monadic type Either<L, R>

Author: android10

app/src/main/kotlin/com/fernandocejas/sample/core/functional/Either.kt

@@ -31,12 +31,28 @@ sealed class Either<out L, out R> {
  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))