fix: add lazy support for iterators

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

iterator/stateless/generic/io.go

@@ -0,0 +1,34 @@
+// 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"
+	L "github.com/IBM/fp-go/io/generic"
+	O "github.com/IBM/fp-go/option"
+	T "github.com/IBM/fp-go/tuple"
+)
+
+// FromLazy returns an iterator on top of a lazy function
+func FromLazy[GU ~func() O.Option[T.Tuple2[GU, U]], LZ ~func() U, U any](l LZ) GU {
+	return F.Pipe1(
+		l,
+		L.Map[LZ, GU](F.Flow2(
+			F.Bind1st(T.MakeTuple2[GU, U], Empty[GU]()),
+			O.Of[T.Tuple2[GU, U]],
+		)),
+	)
+}

iterator/stateless/io.go

@@ -0,0 +1,32 @@
+// 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 (
+	IO "github.com/IBM/fp-go/io"
+	G "github.com/IBM/fp-go/iterator/stateless/generic"
+	L "github.com/IBM/fp-go/lazy"
+)
+
+// FromLazy returns an [Iterator] on top of a lazy function
+func FromLazy[U any](l L.Lazy[U]) Iterator[U] {
+	return G.FromLazy[Iterator[U], L.Lazy[U]](l)
+}
+
+// FromIO returns an [Iterator] on top of an IO function
+func FromIO[U any](io IO.IO[U]) Iterator[U] {
+	return G.FromLazy[Iterator[U], IO.IO[U]](io)
+}

iterator/stateless/io_test.go

@@ -0,0 +1,38 @@
+// 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 (
+	"math/rand"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestIteratorFromLazy(t *testing.T) {
+	num := rand.Int
+
+	cit := FromLazy(num)
+
+	// create arrays twice
+	c1 := ToArray(cit)
+	c2 := ToArray(cit)
+
+	assert.Equal(t, 1, len(c1))
+	assert.Equal(t, 1, len(c2))
+
+	assert.NotEqual(t, c1, c2)
+}