fix: add Ap for iterators

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

iterator/stateless/generic/iterator.go

@@ -68,7 +68,7 @@ func ToArray[GU ~func() O.Option[T.Tuple2[GU, U]], US ~[]U, U any](u GU) US {
 	return Reduce[GU](A.Append[US], A.Empty[US]())(u)
 }
 
-func Map[GV ~func() O.Option[T.Tuple2[GV, V]], GU ~func() O.Option[T.Tuple2[GU, U]], U, V any](f func(U) V) func(ma GU) GV {
+func Map[GV ~func() O.Option[T.Tuple2[GV, V]], GU ~func() O.Option[T.Tuple2[GU, U]], FCT ~func(U) V, U, V any](f FCT) func(ma GU) GV {
 	// pre-declare to avoid cyclic reference
 	var m func(O.Option[T.Tuple2[GU, U]]) O.Option[T.Tuple2[GV, V]]
 
@@ -160,6 +160,7 @@ func MakeBy[GU ~func() O.Option[T.Tuple2[GU, U]], FCT ~func(int) U, U any](n int
 		)),
 	)
 
+	// bootstrap
 	return recurse(0)
 }
 
@@ -167,3 +168,36 @@ func MakeBy[GU ~func() O.Option[T.Tuple2[GU, U]], FCT ~func(int) U, U any](n int
 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))
 }
+
+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 {
+	// pre-declare to avoid cyclic reference
+	var m func(O.Option[T.Tuple2[GU, U]]) O.Option[T.Tuple2[GV, V]]
+
+	recurse := func(ma GU) GV {
+		return F.Nullary2(
+			ma,
+			m,
+		)
+	}
+
+	m = O.Fold(
+		Empty[GV](),
+		func(t T.Tuple2[GU, U]) O.Option[T.Tuple2[GV, V]] {
+			r := recurse(t.F1)
+			return O.MonadFold(f(t.F2), r, F.Flow2(
+				F.Bind1st(T.MakeTuple2[GV, V], r),
+				O.Some[T.Tuple2[GV, V]],
+			))
+		},
+	)
+
+	return recurse
+}
+
+func Filter[GU ~func() O.Option[T.Tuple2[GU, U]], FCT ~func(U) bool, U any](f FCT) func(ma GU) GU {
+	return FilterMap[GU, GU](O.FromPredicate(f))
+}
+
+func Ap[GUV ~func() O.Option[T.Tuple2[GUV, func(U) V]], GV ~func() O.Option[T.Tuple2[GV, V]], GU ~func() O.Option[T.Tuple2[GU, U]], U, V any](ma GU) func(fab GUV) GV {
+	return Chain[GV, GUV](F.Bind1st(MonadMap[GV, GU], ma))
+}

iterator/stateless/iterator.go

@@ -73,6 +73,11 @@ func Flatten[U any](ma Iterator[Iterator[U]]) Iterator[U] {
 	return G.Flatten[Iterator[Iterator[U]], Iterator[U]](ma)
 }
 
+// From constructs an [Iterator] from a set of variadic arguments
+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)
@@ -82,3 +87,18 @@ func MakeBy[FCT ~func(int) U, U any](n int, f FCT) Iterator[U] {
 func Replicate[U any](n int, a U) Iterator[U] {
 	return G.Replicate[Iterator[U]](n, a)
 }
+
+// FilterMap filters and transforms the content of an iterator
+func FilterMap[U, V any](f func(U) O.Option[V]) func(ma Iterator[U]) Iterator[V] {
+	return G.FilterMap[Iterator[V], Iterator[U]](f)
+}
+
+// Filter filters the content of an iterator
+func Filter[U any](f func(U) bool) func(ma Iterator[U]) Iterator[U] {
+	return G.Filter[Iterator[U]](f)
+}
+
+// Ap is the applicative functor for iterators
+func Ap[U, V any](ma Iterator[U]) func(Iterator[func(U) V]) Iterator[V] {
+	return G.Ap[Iterator[func(U) V], Iterator[V]](ma)
+}

iterator/stateless/iterator_test.go

@@ -17,11 +17,13 @@ package stateless
 
 import (
 	"fmt"
+	"math"
 	"testing"
 
 	A "github.com/IBM/fp-go/array"
 	F "github.com/IBM/fp-go/function"
 	"github.com/IBM/fp-go/internal/utils"
+	O "github.com/IBM/fp-go/option"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -38,7 +40,7 @@ func TestIterator(t *testing.T) {
 
 func TestChain(t *testing.T) {
 
-	outer := FromArray[int](A.From(1, 2, 3))
+	outer := From(1, 2, 3)
 
 	inner := func(data int) Iterator[string] {
 		return F.Pipe2(
@@ -58,3 +60,27 @@ func TestChain(t *testing.T) {
 
 	assert.Equal(t, A.From("item[1][0]", "item[1][1]", "item[2][0]", "item[2][1]", "item[3][0]", "item[3][1]"), total)
 }
+
+func isPrimeNumber(num int) bool {
+	if num <= 2 {
+		return true
+	}
+	sq_root := int(math.Sqrt(float64(num)))
+	for i := 2; i <= sq_root; i++ {
+		if num%i == 0 {
+			return false
+		}
+	}
+	return true
+}
+
+func TestFilterMap(t *testing.T) {
+
+	it := F.Pipe2(
+		MakeBy(100, utils.Inc),
+		FilterMap(O.FromPredicate(isPrimeNumber)),
+		ToArray[int],
+	)
+
+	assert.Equal(t, A.From(1, 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97), it)
+}