fix: add ap sample

Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com>

samples/mostly-adequate/chapter10_applicativefunctor_test.go

@@ -0,0 +1,73 @@
+// 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 mostlyadequate
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+
+	R "github.com/IBM/fp-go/context/readerioeither"
+	H "github.com/IBM/fp-go/context/readerioeither/http"
+	F "github.com/IBM/fp-go/function"
+)
+
+type PostItem struct {
+	UserId uint   `json:"userId"`
+	Id     uint   `json:"id"`
+	Title  string `json:"title"`
+	Body   string `json:"body"`
+}
+
+func getTitle(item PostItem) string {
+	return item.Title
+}
+
+func idxToUrl(idx int) string {
+	return fmt.Sprintf("https://jsonplaceholder.typicode.com/posts/%d", idx+1)
+}
+
+func renderString(destinations string) func(string) string {
+	return func(events string) string {
+		return fmt.Sprintf("<div>Destinations: [%s], Events: [%s]</div>", destinations, events)
+	}
+}
+
+func Example_renderPage() {
+	// prepare the http client
+	client := H.MakeClient(http.DefaultClient)
+
+	// get returns the title of the nth item from the REST service
+	get := F.Flow4(
+		idxToUrl,
+		H.MakeGetRequest,
+		H.ReadJson[PostItem](client),
+		R.Map(getTitle),
+	)
+
+	res := F.Pipe2(
+		R.Of(renderString),                // start with a function with 2 unresolved arguments
+		R.Ap[func(string) string](get(1)), // resolve the first argument
+		R.Ap[string](get(2)),              // in parallel resolve the second argument
+	)
+
+	// finally invoke in context and start
+	fmt.Println(res(context.TODO())())
+
+	// Output:
+	// Right[<nil>, string](<div>Destinations: [qui est esse], Events: [ea molestias quasi exercitationem repellat qui ipsa sit aut]</div>)
+
+}