From 56860425c4ce381aa9d0f4474af6383317d9a69f Mon Sep 17 00:00:00 2001
From: Carsten Leue <CarstenLeue@users.noreply.github.com>
Date: Sun, 12 Nov 2023 13:34:27 +0100
Subject: [PATCH] fix: add Flip function (#80)

Signed-off-by: Carsten Leue <carsten.leue@de.ibm.com>
---
 function/flip.go      | 25 +++++++++++++++++++++++++
 function/flip_test.go | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+)
 create mode 100644 function/flip.go
 create mode 100644 function/flip_test.go

diff --git a/function/flip.go b/function/flip.go
new file mode 100644
index 0000000..a721924
--- /dev/null
+++ b/function/flip.go
@@ -0,0 +1,25 @@
+// Copyright (c) 2023 IBM Corp.
+// All rights reserved.
+//
+// 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.
+
+package function
+
+// Flip reverses the order of parameters of a curried function
+func Flip[T1, T2, R any](f func(T1) func(T2) R) func(T2) func(T1) R {
+	return func(t2 T2) func(T1) R {
+		return func(t1 T1) R {
+			return f(t1)(t2)
+		}
+	}
+}
diff --git a/function/flip_test.go b/function/flip_test.go
new file mode 100644
index 0000000..55b0c27
--- /dev/null
+++ b/function/flip_test.go
@@ -0,0 +1,36 @@
+// Copyright (c) 2023 IBM Corp.
+// All rights reserved.
+//
+// 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.
+
+package function
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFlip(t *testing.T) {
+
+	x := Curry2(func(a, b string) string {
+		return fmt.Sprintf("%s:%s", a, b)
+	})
+
+	assert.Equal(t, "a:b", x("a")("b"))
+
+	y := Flip(x)
+
+	assert.Equal(t, "b:a", y("a")("b"))
+}