fix: add first and last

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

iterator/stateless/first.go

@@ -0,0 +1,26 @@
+// 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 stateless
+
+import (
+	G "github.com/IBM/fp-go/iterator/stateless/generic"
+	O "github.com/IBM/fp-go/option"
+)
+
+// First returns the first item in an iterator if such an item exists
+func First[U any](mu Iterator[U]) O.Option[U] {
+	return G.First[Iterator[U]](mu)
+}

iterator/stateless/first_test.go

@@ -0,0 +1,41 @@
+// 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 stateless
+
+import (
+	"testing"
+
+	O "github.com/IBM/fp-go/option"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFirst(t *testing.T) {
+
+	seq := From(1, 2, 3)
+
+	fst := First(seq)
+
+	assert.Equal(t, O.Of(1), fst)
+}
+
+func TestNoFirst(t *testing.T) {
+
+	seq := Empty[int]()
+
+	fst := First(seq)
+
+	assert.Equal(t, O.None[int](), fst)
+}

iterator/stateless/generic/first.go

@@ -0,0 +1,30 @@
+// 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 generic
+
+import (
+	F "github.com/IBM/fp-go/function"
+	O "github.com/IBM/fp-go/option"
+	T "github.com/IBM/fp-go/tuple"
+)
+
+// First returns the first item in an iterator if such an item exists
+func First[GU ~func() O.Option[T.Tuple2[GU, U]], U any](mu GU) O.Option[U] {
+	return F.Pipe1(
+		mu(),
+		O.Map(T.Second[GU, U]),
+	)
+}

iterator/stateless/generic/iterator.go

@@ -49,9 +49,8 @@ func FromArray[GU ~func() O.Option[T.Tuple2[GU, U]], US ~[]U, U any](as US) GU {
 	})(as)
 }
 
-// Reduce applies a function for each value of the iterator with a floating result
-func Reduce[GU ~func() O.Option[T.Tuple2[GU, U]], U, V any](f func(V, U) V, initial V) func(GU) V {
-	return func(as GU) V {
+// reduce applies a function for each value of the iterator with a floating result
+func reduce[GU ~func() O.Option[T.Tuple2[GU, U]], U, V any](as GU, f func(V, U) V, initial V) V {
 	next, ok := O.Unwrap(as())
 	current := initial
 	for ok {
@@ -61,6 +60,10 @@ func Reduce[GU ~func() O.Option[T.Tuple2[GU, U]], U, V any](f func(V, U) V, init
 	}
 	return current
 }
+
+// Reduce applies a function for each value of the iterator with a floating result
+func Reduce[GU ~func() O.Option[T.Tuple2[GU, U]], U, V any](f func(V, U) V, initial V) func(GU) V {
+	return F.Bind23of3(reduce[GU, U, V])(f, initial)
 }
 
 // ToArray converts the iterator to an array

iterator/stateless/generic/last.go

@@ -0,0 +1,27 @@
+// 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 generic
+
+import (
+	F "github.com/IBM/fp-go/function"
+	O "github.com/IBM/fp-go/option"
+	T "github.com/IBM/fp-go/tuple"
+)
+
+// Last returns the last item in an iterator if such an item exists
+func Last[GU ~func() O.Option[T.Tuple2[GU, U]], U any](mu GU) O.Option[U] {
+	return reduce(mu, F.Ignore1of2[O.Option[U]](O.Of[U]), O.None[U]())
+}

iterator/stateless/last.go

@@ -0,0 +1,27 @@
+// 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 stateless
+
+import (
+	G "github.com/IBM/fp-go/iterator/stateless/generic"
+	O "github.com/IBM/fp-go/option"
+)
+
+// Last returns the last item in an iterator if such an item exists
+// Note that the function will consume the [Iterator] in this call completely, to identify the last element. Do not use this for infinite iterators
+func Last[U any](mu Iterator[U]) O.Option[U] {
+	return G.Last[Iterator[U]](mu)
+}

iterator/stateless/last_test.go

@@ -0,0 +1,41 @@
+// 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 stateless
+
+import (
+	"testing"
+
+	O "github.com/IBM/fp-go/option"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestLast(t *testing.T) {
+
+	seq := From(1, 2, 3)
+
+	fst := Last(seq)
+
+	assert.Equal(t, O.Of(3), fst)
+}
+
+func TestNoLast(t *testing.T) {
+
+	seq := Empty[int]()
+
+	fst := Last(seq)
+
+	assert.Equal(t, O.None[int](), fst)
+}