Impl : Impl flatmap

myeonginwoo · Dec 28, 2016 · 216e851 · 216e851
1 parent 9c7ea84
commit 216e851
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Showing 4 changed files with 26 additions and 1 deletion.
diff --git a/Either/src/main/kotlin/LeftProjection.kt b/Either/src/main/kotlin/LeftProjection.kt
@@ -22,4 +22,8 @@ class LeftProjection<out L, out R>(val value: L) {
     fun exists(f: (L) -> Boolean): Boolean {
         return f(value)
     }
+
+    fun <X, R1> flatMap(f: (L) -> Either<X, R1>): Either<X, R1> {
+        return f(value)
+    }
 }
diff --git a/Either/src/main/kotlin/RightProjection.kt b/Either/src/main/kotlin/RightProjection.kt
@@ -22,4 +22,8 @@ class RightProjection<out L, out R>(val value: R) {
     fun exists(f: (R) -> Boolean): Boolean {
         return f(value)
     }
+
+    fun <L1, X> flatMap(f: (R) -> Either<L1, X>): Either<L1, X> {
+        return f(value)
+    }
 }
diff --git a/Either/src/test/kotlin/EitherTest.kt b/Either/src/test/kotlin/EitherTest.kt
@@ -75,7 +75,7 @@ class EitherTest {
         assertEquals(rightEither.fold({ "Left is $it" }, { it * 3 }), 18)
     }
 
-    @Test fun existsTesT() {
+    @Test fun existsTest() {
         val leftEither: Either<String, Int> = Left("test")
         assertEquals(leftEither.left?.exists { it.length == 4 }, true)
         assertEquals(leftEither.left?.exists { it.length > 4 }, false)
@@ -84,4 +84,12 @@ class EitherTest {
         assertEquals(rightEither.right?.exists { it > 5 }, true)
         assertEquals(rightEither.right?.exists { it < 5 }, false)
     }
+
+    @Test fun flatMapTest() {
+        val leftEither: Either<String, Int> = Left("test")
+        assertEquals(leftEither.left?.flatMap { Left<Int, Long>(3) }?.left?.get, 3)
+
+        val rightEither: Either<String, Int> = Right(6)
+        assertEquals(rightEither.right?.flatMap { Right<Int, String>("test") }?.right?.get, "test")
+    }
 }
diff --git a/README.md b/README.md
@@ -70,3 +70,12 @@ val rightEither: Either<String, Int> = Right(6)
 assertEquals(rightEither.right?.exists { it > 5 }, true)
 assertEquals(rightEither.right?.exists { it < 5 }, false)
 ```
+
+flatmap
+```kotlin
+val leftEither: Either<String, Int> = Left("test")
+assertEquals(leftEither.left?.flatMap { Left<Int, Long>(3) }?.left?.get, 3)
+
+val rightEither: Either<String, Int> = Right(6)
+assertEquals(rightEither.right?.flatMap { Right<Int, String>("test") }?.right?.get, "test")
+```