fix: add Take to Iterables

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

iterator/stateless/generic/scan.go

@@ -0,0 +1,39 @@
+// 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"
+)
+
+func Scan[GV ~func() O.Option[T.Tuple2[GV, V]], GU ~func() O.Option[T.Tuple2[GU, U]], FCT ~func(V, U) V, U, V any](f FCT, initial V) func(ma GU) GV {
+	// pre-declare to avoid cyclic reference
+	var recurse func(ma GU, v V) GV
+
+	recurse = func(ma GU, current V) GV {
+		return F.Nullary2(
+			ma,
+			O.Map(func(t T.Tuple2[GU, U]) T.Tuple2[GV, V] {
+				v := f(current, t.F2)
+				return T.MakeTuple2(recurse(t.F1, v), v)
+			}),
+		)
+	}
+
+	return F.Bind2nd(recurse, initial)
+}

iterator/stateless/generic/take.go

@@ -0,0 +1,47 @@
+// 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"
+	N "github.com/IBM/fp-go/number/integer"
+	O "github.com/IBM/fp-go/option"
+	T "github.com/IBM/fp-go/tuple"
+)
+
+func Take[GU ~func() O.Option[T.Tuple2[GU, U]], U any](n int) func(ma GU) GU {
+	// pre-declare to avoid cyclic reference
+	var recurse func(ma GU, idx int) GU
+
+	fromPred := O.FromPredicate(N.Between(0, n))
+
+	recurse = func(ma GU, idx int) GU {
+		return func() O.Option[T.Tuple2[GU, U]] {
+			return F.Pipe2(
+				idx,
+				fromPred,
+				O.Chain(F.Ignore1of1[int](F.Nullary2(
+					ma,
+					O.Map(func(t T.Tuple2[GU, U]) T.Tuple2[GU, U] {
+						return T.MakeTuple2(recurse(t.F1, idx+1), t.F2)
+					}),
+				))),
+			)
+		}
+	}
+
+	return F.Bind2nd(recurse, 0)
+}

iterator/stateless/scan.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"
+)
+
+// Scan takes an [Iterator] and returns a new [Iterator] of the same length, where the values
+// of the new [Iterator] are the result of the application of `f` to the value of the
+// source iterator with the previously accumulated value
+func Scan[FCT ~func(V, U) V, U, V any](f FCT, initial V) func(ma Iterator[U]) Iterator[V] {
+	return G.Scan[Iterator[V], Iterator[U], FCT](f, initial)
+}

iterator/stateless/scan_test.go

@@ -0,0 +1,42 @@
+// 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"
+
+	F "github.com/IBM/fp-go/function"
+	T "github.com/IBM/fp-go/tuple"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestScan(t *testing.T) {
+
+	src := From("a", "b", "c")
+
+	dst := F.Pipe1(
+		src,
+		Scan(func(cur T.Tuple2[int, string], val string) T.Tuple2[int, string] {
+			return T.MakeTuple2(cur.F1+1, val)
+		}, T.MakeTuple2(0, "")),
+	)
+
+	assert.Equal(t, ToArray(From(
+		T.MakeTuple2(1, "a"),
+		T.MakeTuple2(2, "b"),
+		T.MakeTuple2(3, "c"),
+	)), ToArray(dst))
+}

iterator/stateless/take.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 stateless
+
+import (
+	G "github.com/IBM/fp-go/iterator/stateless/generic"
+)
+
+// Take limits the number of values in the [Iterator] to a maximum number
+func Take[U any](n int) func(ma Iterator[U]) Iterator[U] {
+	return G.Take[Iterator[U]](n)
+}

iterator/stateless/take_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 stateless
+
+import (
+	"testing"
+
+	F "github.com/IBM/fp-go/function"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestTake(t *testing.T) {
+
+	total := MakeBy(100, F.Identity[int])
+
+	trimmed := F.Pipe1(
+		total,
+		Take[int](10),
+	)
+
+	assert.Equal(t, ToArray(MakeBy(10, F.Identity[int])), ToArray(trimmed))
+
+}