fix: more iterator functions

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

iterator/stateless/compress.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"
+	T "github.com/IBM/fp-go/tuple"
+)
+
+// Compress returns an [Iterator] that filters elements from a data [Iterator] returning only those that have a corresponding element in selector [Iterator] that evaluates to `true`.
+// Stops when either the data or selectors iterator has been exhausted.
+func Compress[U any](sel Iterator[bool]) func(Iterator[U]) Iterator[U] {
+	return G.Compress[Iterator[U], Iterator[bool], Iterator[T.Tuple2[U, bool]]](sel)
+}

iterator/stateless/compress_test.go

@@ -0,0 +1,35 @@
+// 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"
+
+	A "github.com/IBM/fp-go/array"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCompress(t *testing.T) {
+	// sequence of 5 items
+	data := From(0, 1, 2, 3)
+	// select some of these items
+	selector := From(true, false, false, true)
+	// compressed result
+	compressed := Compress[int](selector)(data)
+
+	assert.Equal(t, A.From(0, 3), ToArray(compressed))
+
+}

iterator/stateless/cycle.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"
+)
+
+// DropWhile creates an [Iterator] that drops elements from the [Iterator] as long as the predicate is true; afterwards, returns every element.
+// Note, the [Iterator] does not produce any output until the predicate first becomes false
+func Cycle[U any](ma Iterator[U]) Iterator[U] {
+	return G.Cycle[Iterator[U]](ma)
+}

iterator/stateless/cycle_test.go

@@ -0,0 +1,33 @@
+// 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"
+
+	A "github.com/IBM/fp-go/array"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCycle(t *testing.T) {
+	// sequence of 5 items
+	items := Take[int](5)(Count(0))
+	// repeat
+	repeated := Take[int](17)(Cycle(items))
+
+	assert.Equal(t, A.From(0, 1, 2, 3, 4, 0, 1, 2, 3, 4, 0, 1, 2, 3, 4, 0, 1), ToArray(repeated))
+
+}

iterator/stateless/dropwhile.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"
+)
+
+// DropWhile creates an [Iterator] that drops elements from the [Iterator] as long as the predicate is true; afterwards, returns every element.
+// Note, the [Iterator] does not produce any output until the predicate first becomes false
+func DropWhile[U any](pred func(U) bool) func(Iterator[U]) Iterator[U] {
+	return G.DropWhile[Iterator[U]](pred)
+}

iterator/stateless/dropwhile_test.go

@@ -0,0 +1,35 @@
+// 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"
+
+	A "github.com/IBM/fp-go/array"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDropWhile(t *testing.T) {
+	// sequence of 5 items
+	data := Take[int](10)(Cycle(From(0, 1, 2, 3)))
+
+	total := DropWhile(func(data int) bool {
+		return data <= 2
+	})(data)
+
+	assert.Equal(t, A.From(3, 0, 1, 2, 3, 0, 1), ToArray(total))
+
+}

iterator/stateless/generic/compress.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"
+	O "github.com/IBM/fp-go/option"
+	T "github.com/IBM/fp-go/tuple"
+)
+
+// Compress returns an [Iterator] that filters elements from a data [Iterator] returning only those that have a corresponding element in selector [Iterator] that evaluates to `true`.
+// Stops when either the data or selectors iterator has been exhausted.
+func Compress[GU ~func() O.Option[T.Tuple2[GU, U]], GB ~func() O.Option[T.Tuple2[GB, bool]], CS ~func() O.Option[T.Tuple2[CS, T.Tuple2[U, bool]]], U any](sel GB) func(GU) GU {
+	return F.Flow2(
+		Zip[GU, GB, CS](sel),
+		FilterMap[GU, CS](F.Flow2(
+			O.FromPredicate(T.Second[U, bool]),
+			O.Map(T.First[U, bool]),
+		)),
+	)
+}

iterator/stateless/generic/cycle.go

@@ -0,0 +1,43 @@
+// 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 Cycle[GU ~func() O.Option[T.Tuple2[GU, U]], U any](ma GU) GU {
+	// avoid cyclic references
+	var m func(O.Option[T.Tuple2[GU, U]]) O.Option[T.Tuple2[GU, U]]
+
+	recurse := func(mu GU) GU {
+		return F.Nullary2(
+			mu,
+			m,
+		)
+	}
+
+	m = O.Fold(func() O.Option[T.Tuple2[GU, U]] {
+		return recurse(ma)()
+	}, F.Flow2(
+		T.Map2(recurse, F.Identity[U]),
+		O.Of[T.Tuple2[GU, U]],
+	))
+
+	return recurse(ma)
+}

iterator/stateless/generic/dropwhile.go

@@ -0,0 +1,49 @@
+// 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"
+	P "github.com/IBM/fp-go/predicate"
+	T "github.com/IBM/fp-go/tuple"
+)
+
+// DropWhile creates an [Iterator] that drops elements from the [Iterator] as long as the predicate is true; afterwards, returns every element.
+// Note, the [Iterator] does not produce any output until the predicate first becomes false
+func DropWhile[GU ~func() O.Option[T.Tuple2[GU, U]], U any](pred func(U) bool) func(GU) GU {
+	// avoid cyclic references
+	var m func(O.Option[T.Tuple2[GU, U]]) O.Option[T.Tuple2[GU, U]]
+
+	fromPred := O.FromPredicate(P.Not(P.ContraMap(T.Second[GU, U])(pred)))
+
+	recurse := func(mu GU) GU {
+		return F.Nullary2(
+			mu,
+			m,
+		)
+	}
+
+	m = O.Chain(func(t T.Tuple2[GU, U]) O.Option[T.Tuple2[GU, U]] {
+		return F.Pipe2(
+			t,
+			fromPred,
+			O.Fold(recurse(t.F1), O.Of[T.Tuple2[GU, U]]),
+		)
+	})
+
+	return recurse
+}

iterator/stateless/generic/iterator.go

@@ -20,7 +20,7 @@ import (
 	F "github.com/IBM/fp-go/function"
 	"github.com/IBM/fp-go/internal/utils"
 	IO "github.com/IBM/fp-go/iooption/generic"
-	N "github.com/IBM/fp-go/number/integer"
+	N "github.com/IBM/fp-go/number"
 	O "github.com/IBM/fp-go/option"
 	T "github.com/IBM/fp-go/tuple"
 )
@@ -135,38 +135,49 @@ func Flatten[GV ~func() O.Option[T.Tuple2[GV, GU]], GU ~func() O.Option[T.Tuple2
 	return MonadChain(ma, F.Identity[GU])
 }
 
-// MakeBy returns an [Iterator] with `n` elements initialized with `f(i)`
-func MakeBy[GU ~func() O.Option[T.Tuple2[GU, U]], FCT ~func(int) U, U any](n int, f FCT) GU {
+// MakeBy returns an [Iterator] with an infinite number of elements initialized with `f(i)`
+func MakeBy[GU ~func() O.Option[T.Tuple2[GU, U]], FCT ~func(int) U, U any](f FCT) GU {
 
 	var m func(int) O.Option[T.Tuple2[GU, U]]
 
 	recurse := func(i int) GU {
-		return func() O.Option[T.Tuple2[GU, U]] {
-			return F.Pipe1(
-				i,
-				m,
-			)
-		}
+		return F.Nullary2(
+			F.Constant(i),
+			m,
+		)
 	}
 
-	m = F.Flow2(
-		O.FromPredicate(N.Between(0, n)),
-		O.Map(F.Flow2(
-			T.Replicate2[int],
-			T.Map2(F.Flow2(
-				utils.Inc,
-				recurse),
-				f),
-		)),
+	m = F.Flow3(
+		T.Replicate2[int],
+		T.Map2(F.Flow2(
+			utils.Inc,
+			recurse),
+			f),
+		O.Of[T.Tuple2[GU, U]],
 	)
 
 	// bootstrap
 	return recurse(0)
 }
 
-// Replicate creates an [Iterator] containing a value repeated the specified number of times.
-func Replicate[GU ~func() O.Option[T.Tuple2[GU, U]], U any](n int, a U) GU {
-	return MakeBy[GU](n, F.Constant1[int](a))
+// Replicate creates an infinite [Iterator] containing a value.
+func Replicate[GU ~func() O.Option[T.Tuple2[GU, U]], U any](a U) GU {
+	return MakeBy[GU](F.Constant1[int](a))
+}
+
+// Repeat creates an [Iterator] containing a value repeated the specified number of times.
+// Alias of [Replicate] combined with [Take]
+func Repeat[GU ~func() O.Option[T.Tuple2[GU, U]], U any](n int, a U) GU {
+	return F.Pipe2(
+		a,
+		Replicate[GU],
+		Take[GU](n),
+	)
+}
+
+// Count creates an [Iterator] containing a consecutive sequence of integers starting with the provided start value
+func Count[GU ~func() O.Option[T.Tuple2[GU, int]]](start int) GU {
+	return MakeBy[GU](N.Add(start))
 }
 
 func FilterMap[GV ~func() O.Option[T.Tuple2[GV, V]], GU ~func() O.Option[T.Tuple2[GU, U]], FCT ~func(U) O.Option[V], U, V any](f FCT) func(ma GU) GV {

iterator/stateless/generic/scan.go

@@ -21,19 +21,25 @@ import (
 	T "github.com/IBM/fp-go/tuple"
 )
 
+func apTuple[A, B any](t T.Tuple2[func(A) B, A]) T.Tuple2[B, A] {
+	return T.MakeTuple2(t.F1(t.F2), t.F2)
+}
+
 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
+	var m func(GU) func(V) GV
 
-	recurse = func(ma GU, current 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)
-			}),
+			O.Map(F.Flow2(
+				T.Map2(m, F.Bind1st(f, current)),
+				apTuple[V, GV],
+			)),
 		)
 	}
 
+	m = F.Curry2(recurse)
+
 	return F.Bind2nd(recurse, initial)
 }

iterator/stateless/generic/take.go

@@ -29,18 +29,14 @@ func Take[GU ~func() O.Option[T.Tuple2[GU, U]], U any](n int) func(ma GU) 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.Nullary3(
+			F.Constant(idx),
+			fromPred,
+			O.Chain(F.Ignore1of1[int](F.Nullary2(
+				ma,
+				O.Map(T.Map2(F.Bind2nd(recurse, idx+1), F.Identity[U])),
+			))),
+		)
 	}
 
 	return F.Bind2nd(recurse, 0)

iterator/stateless/iterator.go

@@ -78,14 +78,14 @@ func From[U any](data ...U) Iterator[U] {
 	return G.From[Iterator[U]](data...)
 }
 
-// MakeBy returns an [Iterator] with `n` elements initialized with `f(i)`
-func MakeBy[FCT ~func(int) U, U any](n int, f FCT) Iterator[U] {
-	return G.MakeBy[Iterator[U]](n, f)
+// MakeBy returns an [Iterator] with an infinite number of elements initialized with `f(i)`
+func MakeBy[FCT ~func(int) U, U any](f FCT) Iterator[U] {
+	return G.MakeBy[Iterator[U]](f)
 }
 
-// Replicate creates an [Iterator] containing a value repeated the specified number of times.
-func Replicate[U any](n int, a U) Iterator[U] {
-	return G.Replicate[Iterator[U]](n, a)
+// Replicate creates an [Iterator] containing a value repeated an infinite number of times.
+func Replicate[U any](a U) Iterator[U] {
+	return G.Replicate[Iterator[U]](a)
 }
 
 // FilterMap filters and transforms the content of an iterator
@@ -107,3 +107,14 @@ func Ap[V, U any](ma Iterator[U]) func(Iterator[func(U) V]) Iterator[V] {
 func MonadAp[V, U any](fab Iterator[func(U) V], ma Iterator[U]) Iterator[V] {
 	return G.MonadAp[Iterator[func(U) V], Iterator[V]](fab, ma)
 }
+
+// Repeat creates an [Iterator] containing a value repeated the specified number of times.
+// Alias of [Replicate]
+func Repeat[U any](n int, a U) Iterator[U] {
+	return G.Repeat[Iterator[U]](n, a)
+}
+
+// Count creates an [Iterator] containing a consecutive sequence of integers starting with the provided start value
+func Count(start int) Iterator[int] {
+	return G.Count[Iterator[int]](start)
+}

iterator/stateless/iterator_test.go

@@ -76,8 +76,9 @@ func isPrimeNumber(num int) bool {
 
 func TestFilterMap(t *testing.T) {
 
-	it := F.Pipe2(
-		MakeBy(100, utils.Inc),
+	it := F.Pipe3(
+		MakeBy(utils.Inc),
+		Take[int](100),
 		FilterMap(O.FromPredicate(isPrimeNumber)),
 		ToArray[int],
 	)

iterator/stateless/take_test.go

@@ -18,19 +18,20 @@ package stateless
 import (
 	"testing"
 
+	A "github.com/IBM/fp-go/array"
 	F "github.com/IBM/fp-go/function"
 	"github.com/stretchr/testify/assert"
 )
 
 func TestTake(t *testing.T) {
 
-	total := MakeBy(100, F.Identity[int])
+	total := MakeBy(F.Identity[int])
 
 	trimmed := F.Pipe1(
 		total,
 		Take[int](10),
 	)
 
-	assert.Equal(t, ToArray(MakeBy(10, F.Identity[int])), ToArray(trimmed))
+	assert.Equal(t, A.MakeBy(10, F.Identity[int]), ToArray(trimmed))
 
 }