fix: add Filter and FilterMap

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

v2/context/readerioresult/filter.go

@@ -18,6 +18,10 @@ package readerioresult
 import (
 	"context"
 
+	"github.com/IBM/fp-go/v2/array"
+	"github.com/IBM/fp-go/v2/internal/witherable"
+	"github.com/IBM/fp-go/v2/iterator/iter"
+	"github.com/IBM/fp-go/v2/option"
 	RIOR "github.com/IBM/fp-go/v2/readerioresult"
 )
 
@@ -49,3 +53,43 @@ import (
 func FilterOrElse[A any](pred Predicate[A], onFalse func(A) error) Operator[A, A] {
 	return RIOR.FilterOrElse[context.Context](pred, onFalse)
 }
+
+//go:inline
+func Filter[A, HKTA any](
+	filter func(Predicate[A]) Endomorphism[HKTA],
+) func(Predicate[A]) Operator[HKTA, HKTA] {
+	return witherable.Filter(
+		Map,
+		filter,
+	)
+}
+
+//go:inline
+func FilterArray[A any](p Predicate[A]) Operator[[]A, []A] {
+	return Filter(array.Filter[A])(p)
+}
+
+//go:inline
+func FilterIter[A any](p Predicate[A]) Operator[Seq[A], Seq[A]] {
+	return Filter(iter.Filter[A])(p)
+}
+
+//go:inline
+func FilterMap[A, B, HKTA, HKTB any](
+	filter func(option.Kleisli[A, B]) Reader[HKTA, HKTB],
+) func(option.Kleisli[A, B]) Operator[HKTA, HKTB] {
+	return witherable.FilterMap(
+		Map,
+		filter,
+	)
+}
+
+//go:inline
+func FilterMapArray[A, B any](p option.Kleisli[A, B]) Operator[[]A, []B] {
+	return FilterMap(array.FilterMap[A, B])(p)
+}
+
+//go:inline
+func FilterMapIter[A, B any](p option.Kleisli[A, B]) Operator[Seq[A], Seq[B]] {
+	return FilterMap(iter.FilterMap[A, B])(p)
+}

v2/context/readerioresult/type.go

@@ -17,6 +17,7 @@ package readerioresult
 
 import (
 	"context"
+	"iter"
 
 	"github.com/IBM/fp-go/v2/consumer"
 	"github.com/IBM/fp-go/v2/context/ioresult"
@@ -220,4 +221,6 @@ type (
 	// The first element is the CancelFunc that should be called to release resources.
 	// The second element is the new Context that was created.
 	ContextCancel = Pair[context.CancelFunc, context.Context]
+
+	Seq[A any] = iter.Seq[A]
 )

v2/internal/filterable/types.go

@@ -0,0 +1,15 @@
+package filterable
+
+import (
+	"github.com/IBM/fp-go/v2/option"
+	"github.com/IBM/fp-go/v2/pair"
+)
+
+type (
+	Option[A any]       = option.Option[A]
+	Separated[A, B any] = pair.Pair[A, B]
+
+	FilterType[A, HKTA any] = func(func(A) bool) func(HKTA) HKTA
+
+	FilterMapType[A, B, HKTA, HKTB any] = func(func(A) Option[B]) func(HKTA) HKTB
+)

v2/internal/witherable/filter.go

@@ -0,0 +1,27 @@
+package witherable
+
+import (
+	"github.com/IBM/fp-go/v2/function"
+	"github.com/IBM/fp-go/v2/internal/filterable"
+	"github.com/IBM/fp-go/v2/internal/functor"
+)
+
+func Filter[A, HKT_G_A, HKT_F_HKT_G_A any](
+	fmap functor.MapType[HKT_G_A, HKT_G_A, HKT_F_HKT_G_A, HKT_F_HKT_G_A],
+	ffilter filterable.FilterType[A, HKT_G_A],
+) func(func(A) bool) func(HKT_F_HKT_G_A) HKT_F_HKT_G_A {
+	return function.Flow2(
+		ffilter,
+		fmap,
+	)
+}
+
+func FilterMap[A, B, HKT_G_A, HKT_G_B, HKT_F_HKT_G_A, HKT_F_HKT_G_B any](
+	fmap functor.MapType[HKT_G_A, HKT_G_B, HKT_F_HKT_G_A, HKT_F_HKT_G_B],
+	ffilter filterable.FilterMapType[A, B, HKT_G_A, HKT_G_B],
+) func(func(A) Option[B]) func(HKT_F_HKT_G_A) HKT_F_HKT_G_B {
+	return function.Flow2(
+		ffilter,
+		fmap,
+	)
+}

v2/internal/witherable/partition.go

@@ -0,0 +1 @@
+package witherable

v2/internal/witherable/type.go

@@ -0,0 +1,7 @@
+package witherable
+
+import "github.com/IBM/fp-go/v2/option"
+
+type (
+	Option[A any] = option.Option[A]
+)