Add bimap and fold to Result (#64)

* Add bimap to Result

Signed-off-by: Corina Usher <coughlac@hotmail.com>
Signed-off-by: Corina Usher <corina.usher@example.com>

* Add fold to Result

Signed-off-by: Corina Usher <coughlac@hotmail.com>
Signed-off-by: Corina Usher <corina.usher@example.com>

---------

Signed-off-by: Corina Usher <coughlac@hotmail.com>
Signed-off-by: Corina Usher <corina.usher@example.com>
Co-authored-by: Corina Usher <corina.usher@example.com>

Author: coughlac

result4k/core/src/main/kotlin/dev/forkhandles/result4k/result.kt

@@ -51,6 +51,21 @@ inline fun <T, Tʹ, E> Result<T, E>.flatMap(f: (T) -> Result<Tʹ, E>): Result<T
 inline fun <T, E, Eʹ> Result<T, E>.mapFailure(f: (E) -> Eʹ): Result<T, Eʹ> =
     flatMapFailure { reason -> Failure(f(reason)) }
 
+/**
+ * Map a function, f, over the `value` of a successful `Result`
+ * and a function, g, over the `reason` of an unsuccessful `Result`.
+ */
+inline fun <T, Tʹ, E, Eʹ> Result<T, E>.bimap(f: (T) -> Tʹ, g: (E) -> Eʹ): Result<Tʹ, Eʹ> =
+    map { f(it) }.mapFailure { g(it) }
+
+/**
+ * Fold a function, f, over the `value` of a successful `Result`
+ * and a function, g, over the `reason` of an unsuccessful `Result`
+ * where both functions result in a value of the same type, returning a plain value.
+ */
+inline fun <T, E, Tʹ> Result<T, E>.fold(f: (T) -> Tʹ, g: (E) -> Tʹ): Tʹ =
+    bimap(f, g).get()
+
 /**
  * Flat-map a function over the `reason` of an unsuccessful `Result`.
  */

result4k/core/src/test/kotlin/dev/forkhandles/result4k/bimap_tests.kt

@@ -0,0 +1,25 @@
+package dev.forkhandles.result4k
+
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+import kotlin.test.fail
+
+class BiMapTests {
+    @Test
+    fun `bimap success`() {
+        val result = Success(123).bimap(
+            { "This is the successful result: ${it + 1}" },
+            { fail("should not be called for a success") })
+
+        assertEquals(Success("This is the successful result: 124"), result)
+    }
+
+    @Test
+    fun `bimap failure`() {
+        val result = Failure(123).bimap(
+            { fail("should not be called for a failure") },
+            { "This is the failed result: ${it + 1}" })
+
+        assertEquals(Failure("This is the failed result: 124"), result)
+    }
+}

result4k/core/src/test/kotlin/dev/forkhandles/result4k/fold_tests.kt

@@ -0,0 +1,19 @@
+package dev.forkhandles.result4k
+
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+import kotlin.test.fail
+
+class FoldTests {
+    @Test
+    fun `fold success`() {
+        val result = Success(123).fold({ "A value of: ${(it + 1)}" }, { fail("should not be called for a success") })
+        assertEquals("A value of: 124", result)
+    }
+
+    @Test
+    fun `fold failure`() {
+        val result = Failure(123).fold({ fail("should not be called for a failure") }, { "A value of: ${(it + 1)}" })
+        assertEquals("A value of: 124", result)
+    }
+}