Add zip functions

src/main/kotlin/com/github/michaelbull/result/Zip.kt

@@ -0,0 +1,93 @@
+package com.github.michaelbull.result
+
+private typealias Producer<T, E> = () -> Result<T, E>
+
+/**
+ * Apply a [transformation][transform] to two [Results][Result], if both [Results][Result] are [Ok].
+ * If not, the first argument which is an [Err] will propagate through.
+ *
+ * - Elm: http://package.elm-lang.org/packages/elm-lang/core/latest/Result#map2
+ */
+inline fun <V1, V2, E, U> zip(
+    result1: Producer<V1, E>,
+    result2: Producer<V2, E>,
+    transform: (V1, V2) -> U
+): Result<U, E> {
+    return result1().flatMap { v1 ->
+        result2().map { v2 ->
+            transform(v1, v2)
+        }
+    }
+}
+
+/**
+ * Apply a [transformation][transform] to three [Results][Result], if all [Results][Result] are [Ok].
+ * If not, the first argument which is an [Err] will propagate through.
+ *
+ * - Elm: http://package.elm-lang.org/packages/elm-lang/core/latest/Result#map3
+ */
+inline fun <V1, V2, V3, E, U> zip(
+    result1: Producer<V1, E>,
+    result2: Producer<V2, E>,
+    result3: Producer<V3, E>,
+    transform: (V1, V2, V3) -> U
+): Result<U, E> {
+    return result1().flatMap { v1 ->
+        result2().flatMap { v2 ->
+            result3().map { v3 ->
+                transform(v1, v2, v3)
+            }
+        }
+    }
+}
+
+/**
+ * Apply a [transformation][transform] to four [Results][Result], if all [Results][Result] are [Ok].
+ * If not, the first argument which is an [Err] will propagate through.
+ *
+ * - Elm: http://package.elm-lang.org/packages/elm-lang/core/latest/Result#map4
+ */
+inline fun <V1, V2, V3, V4, E, U> zip(
+    result1: Producer<V1, E>,
+    result2: Producer<V2, E>,
+    result3: Producer<V3, E>,
+    result4: Producer<V4, E>,
+    transform: (V1, V2, V3, V4) -> U
+): Result<U, E> {
+    return result1().flatMap { v1 ->
+        result2().flatMap { v2 ->
+            result3().flatMap { v3 ->
+                result4().map { v4 ->
+                    transform(v1, v2, v3, v4)
+                }
+            }
+        }
+    }
+}
+
+/**
+ * Apply a [transformation][transform] to five [Results][Result], if all [Results][Result] are [Ok].
+ * If not, the first argument which is an [Err] will propagate through.
+ *
+ * - Elm: http://package.elm-lang.org/packages/elm-lang/core/latest/Result#map5
+ */
+inline fun <V1, V2, V3, V4, V5, E, U> zip(
+    result1: Producer<V1, E>,
+    result2: Producer<V2, E>,
+    result3: Producer<V3, E>,
+    result4: Producer<V4, E>,
+    result5: Producer<V5, E>,
+    transform: (V1, V2, V3, V4, V5) -> U
+): Result<U, E> {
+    return result1().flatMap { v1 ->
+        result2().flatMap { v2 ->
+            result3().flatMap { v3 ->
+                result4().flatMap { v4 ->
+                    result5().map { v5 ->
+                        transform(v1, v2, v3, v4, v5)
+                    }
+                }
+            }
+        }
+    }
+}