fix: implement FilterChain

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

array/array.go

@@ -108,10 +108,16 @@ func MonadFilterMap[A, B any](fa []A, f func(a A) O.Option[B]) []B {
 	return G.MonadFilterMap[[]A, []B](fa, f)
 }
 
+// FilterChain maps an array with an iterating function that returns an [O.Option] and it keeps only the Some values discarding the Nones.
 func FilterMap[A, B any](f func(a A) O.Option[B]) func([]A) []B {
 	return G.FilterMap[[]A, []B](f)
 }
 
+// FilterChain maps an array with an iterating function that returns an [O.Option] of an array. It keeps only the Some values discarding the Nones and then flattens the result.
+func FilterChain[A, B any](f func(A) O.Option[[]B]) func([]A) []B {
+	return G.FilterChain[[]A](f)
+}
+
 func FilterMapRef[A, B any](pred func(a *A) bool, f func(a *A) B) func([]A) []B {
 	return func(fa []A) []B {
 		return filterMapRef(fa, pred, f)
@@ -237,7 +243,7 @@ func Intercalate[A any](m M.Monoid[A]) func(A) func([]A) A {
 }
 
 func Flatten[A any](mma [][]A) []A {
-	return MonadChain(mma, F.Identity[[]A])
+	return G.Flatten(mma)
 }
 
 func Slice[A any](low, high int) func(as []A) []A {

array/array_test.go

@@ -16,6 +16,7 @@
 package array
 
 import (
+	"fmt"
 	"strings"
 	"testing"
 
@@ -142,3 +143,33 @@ func TestPartition(t *testing.T) {
 	assert.Equal(t, T.MakeTuple2(Empty[int](), Empty[int]()), Partition(pred)(Empty[int]()))
 	assert.Equal(t, T.MakeTuple2(From(1), From(3)), Partition(pred)(From(1, 3)))
 }
+
+func TestFilterChain(t *testing.T) {
+	src := From(1, 2, 3)
+
+	f := func(i int) O.Option[[]string] {
+		if i%2 != 0 {
+			return O.Of(From(fmt.Sprintf("a%d", i), fmt.Sprintf("b%d", i)))
+		}
+		return O.None[[]string]()
+	}
+
+	res := FilterChain(f)(src)
+
+	assert.Equal(t, From("a1", "b1", "a3", "b3"), res)
+}
+
+func TestFilterMap(t *testing.T) {
+	src := From(1, 2, 3)
+
+	f := func(i int) O.Option[string] {
+		if i%2 != 0 {
+			return O.Of(fmt.Sprintf("a%d", i))
+		}
+		return O.None[string]()
+	}
+
+	res := FilterMap(f)(src)
+
+	assert.Equal(t, From("a1", "a3"), res)
+}

array/generic/array.go

@@ -118,6 +118,17 @@ func MonadFilterMap[GA ~[]A, GB ~[]B, A, B any](fa GA, f func(a A) O.Option[B])
 	return filterMap[GA, GB](fa, f)
 }
 
+func FilterChain[GA ~[]A, GB ~[]B, A, B any](f func(a A) O.Option[GB]) func(GA) GB {
+	return F.Flow2(
+		FilterMap[GA, []GB](f),
+		Flatten[[]GB],
+	)
+}
+
+func Flatten[GAA ~[]GA, GA ~[]A, A any](mma GAA) GA {
+	return MonadChain(mma, F.Identity[GA])
+}
+
 func FilterMap[GA ~[]A, GB ~[]B, A, B any](f func(a A) O.Option[B]) func(GA) GB {
 	return F.Bind2nd(MonadFilterMap[GA, GB, A, B], f)
 }

endomorphism/monoid.go

@@ -21,16 +21,12 @@ import (
 	S "github.com/IBM/fp-go/semigroup"
 )
 
-func concat[A any](first, second func(A) A) func(A) A {
-	return F.Flow2(first, second)
-}
-
 // Semigroup for the Endomorphism where the `concat` operation is the usual function composition.
 func Semigroup[A any]() S.Semigroup[func(A) A] {
-	return S.MakeSemigroup(concat[A])
+	return S.MakeSemigroup(F.Flow2[func(A) A, func(A) A])
 }
 
 // Monoid for the Endomorphism where the `concat` operation is the usual function composition.
 func Monoid[A any]() M.Monoid[func(A) A] {
-	return M.MakeMonoid(concat[A], F.Identity[A])
+	return M.MakeMonoid(F.Flow2[func(A) A, func(A) A], F.Identity[A])
 }

iterator/stateless/generic/iterator.go

@@ -219,3 +219,10 @@ func Ap[GUV ~func() O.Option[T.Tuple2[GUV, func(U) V]], GV ~func() O.Option[T.Tu
 func MonadAp[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](fab GUV, ma GU) GV {
 	return Ap[GUV, GV, GU](ma)(fab)
 }
+
+func FilterChain[GVV ~func() O.Option[T.Tuple2[GVV, GV]], GV ~func() O.Option[T.Tuple2[GV, V]], GU ~func() O.Option[T.Tuple2[GU, U]], FCT ~func(U) O.Option[GV], U, V any](f FCT) func(ma GU) GV {
+	return F.Flow2(
+		FilterMap[GVV, GU](f),
+		Flatten[GVV],
+	)
+}

iterator/stateless/iterator.go

@@ -118,3 +118,8 @@ func Repeat[U any](n int, a U) Iterator[U] {
 func Count(start int) Iterator[int] {
 	return G.Count[Iterator[int]](start)
 }
+
+// FilterChain filters and transforms the content of an iterator
+func FilterChain[U, V any](f func(U) O.Option[Iterator[V]]) func(ma Iterator[U]) Iterator[V] {
+	return G.FilterChain[Iterator[Iterator[V]], Iterator[V], Iterator[U]](f)
+}

record/doc.go

@@ -0,0 +1,17 @@
+// 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 record contains monadic operations for maps as well as a rich set of utility functions
+package record

record/generic/monoid.go

@@ -16,6 +16,7 @@
 package generic
 
 import (
+	F "github.com/IBM/fp-go/function"
 	M "github.com/IBM/fp-go/monoid"
 	S "github.com/IBM/fp-go/semigroup"
 )
@@ -26,3 +27,17 @@ func UnionMonoid[N ~map[K]V, K comparable, V any](s S.Semigroup[V]) M.Monoid[N]
 		Empty[N](),
 	)
 }
+
+func UnionLastMonoid[N ~map[K]V, K comparable, V any]() M.Monoid[N] {
+	return M.MakeMonoid(
+		unionLast[N],
+		Empty[N](),
+	)
+}
+
+func UnionFirstMonoid[N ~map[K]V, K comparable, V any]() M.Monoid[N] {
+	return M.MakeMonoid(
+		F.Swap(unionLast[N]),
+		Empty[N](),
+	)
+}

record/generic/record.go

@@ -19,6 +19,7 @@ import (
 	F "github.com/IBM/fp-go/function"
 	G "github.com/IBM/fp-go/internal/record"
 	Mg "github.com/IBM/fp-go/magma"
+	Mo "github.com/IBM/fp-go/monoid"
 	O "github.com/IBM/fp-go/option"
 	T "github.com/IBM/fp-go/tuple"
 )
@@ -82,6 +83,34 @@ func MonadMap[M ~map[K]V, N ~map[K]R, K comparable, V, R any](r M, f func(V) R)
 	return MonadMapWithIndex[M, N](r, F.Ignore1of2[K](f))
 }
 
+func MonadChainWithIndex[M ~map[K]V1, N ~map[K]V2, K comparable, V1, V2 any](m Mo.Monoid[N], r M, f func(K, V1) N) N {
+	return G.ReduceWithIndex(r, func(k K, dst N, b V1) N {
+		return m.Concat(dst, f(k, b))
+	}, m.Empty())
+}
+
+func MonadChain[M ~map[K]V1, N ~map[K]V2, K comparable, V1, V2 any](m Mo.Monoid[N], r M, f func(V1) N) N {
+	return G.Reduce(r, func(dst N, b V1) N {
+		return m.Concat(dst, f(b))
+	}, m.Empty())
+}
+
+func ChainWithIndex[M ~map[K]V1, N ~map[K]V2, K comparable, V1, V2 any](m Mo.Monoid[N]) func(func(K, V1) N) func(M) N {
+	return func(f func(K, V1) N) func(M) N {
+		return func(ma M) N {
+			return MonadChainWithIndex(m, ma, f)
+		}
+	}
+}
+
+func Chain[M ~map[K]V1, N ~map[K]V2, K comparable, V1, V2 any](m Mo.Monoid[N]) func(func(V1) N) func(M) N {
+	return func(f func(V1) N) func(M) N {
+		return func(ma M) N {
+			return MonadChain(m, ma, f)
+		}
+	}
+}
+
 func MonadMapWithIndex[M ~map[K]V, N ~map[K]R, K comparable, V, R any](r M, f func(K, V) R) N {
 	return G.ReduceWithIndex(r, func(k K, dst N, v V) N {
 		return upsertAtReadWrite(dst, k, f(k, v))
@@ -114,15 +143,14 @@ func MapRefWithIndex[M ~map[K]V, N ~map[K]R, K comparable, V, R any](f func(K, *
 	return F.Bind2nd(MonadMapRefWithIndex[M, N, K, V, R], f)
 }
 
-func lookup[M ~map[K]V, K comparable, V any](r M, k K) O.Option[V] {
-	if val, ok := r[k]; ok {
-		return O.Some(val)
-	}
-	return O.None[V]()
-}
-
 func Lookup[M ~map[K]V, K comparable, V any](k K) func(M) O.Option[V] {
-	return F.Bind2nd(lookup[M, K, V], k)
+	n := O.None[V]()
+	return func(m M) O.Option[V] {
+		if val, ok := m[k]; ok {
+			return O.Some(val)
+		}
+		return n
+	}
 }
 
 func Has[M ~map[K]V, K comparable, V any](k K, r M) bool {
@@ -161,6 +189,31 @@ func union[M ~map[K]V, K comparable, V any](m Mg.Magma[V], left M, right M) M {
 	return result
 }
 
+func unionLast[M ~map[K]V, K comparable, V any](left M, right M) M {
+	lenLeft := len(left)
+
+	if lenLeft == 0 {
+		return right
+	}
+
+	lenRight := len(right)
+	if lenRight == 0 {
+		return left
+	}
+
+	result := make(M, lenLeft+lenRight)
+
+	for k, v := range left {
+		result[k] = v
+	}
+
+	for k, v := range right {
+		result[k] = v
+	}
+
+	return result
+}
+
 func Union[M ~map[K]V, K comparable, V any](m Mg.Magma[V]) func(M) func(M) M {
 	return func(right M) func(M) M {
 		return func(left M) M {
@@ -169,6 +222,22 @@ func Union[M ~map[K]V, K comparable, V any](m Mg.Magma[V]) func(M) func(M) M {
 	}
 }
 
+func UnionLast[M ~map[K]V, K comparable, V any](right M) func(M) M {
+	return func(left M) M {
+		return unionLast(left, right)
+	}
+}
+
+func Merge[M ~map[K]V, K comparable, V any](right M) func(M) M {
+	return UnionLast(right)
+}
+
+func UnionFirst[M ~map[K]V, K comparable, V any](right M) func(M) M {
+	return func(left M) M {
+		return unionLast(right, left)
+	}
+}
+
 func Empty[M ~map[K]V, K comparable, V any]() M {
 	return make(M)
 }
@@ -269,6 +338,33 @@ func FilterMap[M ~map[K]V1, N ~map[K]V2, K comparable, V1, V2 any](f func(V1) O.
 	return F.Bind2nd(filterMapWithIndex[M, N, K, V1, V2], F.Ignore1of2[K](f))
 }
 
+// Flatten converts a nested map into a regular map
+func Flatten[M ~map[K]N, N ~map[K]V, K comparable, V any](m Mo.Monoid[N]) func(M) N {
+	return Chain[M, N](m)(F.Identity[N])
+}
+
+// FilterChainWithIndex creates a new map with only the elements for which the transformation function creates a Some
+func FilterChainWithIndex[M ~map[K]V1, N ~map[K]V2, K comparable, V1, V2 any](m Mo.Monoid[N]) func(func(K, V1) O.Option[N]) func(M) N {
+	flatten := Flatten[map[K]N, N](m)
+	return func(f func(K, V1) O.Option[N]) func(M) N {
+		return F.Flow2(
+			FilterMapWithIndex[M, map[K]N](f),
+			flatten,
+		)
+	}
+}
+
+// FilterChain creates a new map with only the elements for which the transformation function creates a Some
+func FilterChain[M ~map[K]V1, N ~map[K]V2, K comparable, V1, V2 any](m Mo.Monoid[N]) func(func(V1) O.Option[N]) func(M) N {
+	flatten := Flatten[map[K]N, N](m)
+	return func(f func(V1) O.Option[N]) func(M) N {
+		return F.Flow2(
+			FilterMap[M, map[K]N](f),
+			flatten,
+		)
+	}
+}
+
 // IsNil checks if the map is set to nil
 func IsNil[M ~map[K]V, K comparable, V any](m M) bool {
 	return m == nil

record/generic/semigroup.go

@@ -20,8 +20,19 @@ import (
 )
 
 func UnionSemigroup[N ~map[K]V, K comparable, V any](s S.Semigroup[V]) S.Semigroup[N] {
-	union := Union[N, K, V](s)
 	return S.MakeSemigroup(func(first N, second N) N {
-		return union(second)(first)
+		return union(s, first, second)
+	})
+}
+
+func UnionLastSemigroup[N ~map[K]V, K comparable, V any]() S.Semigroup[N] {
+	return S.MakeSemigroup(func(first N, second N) N {
+		return unionLast(first, second)
+	})
+}
+
+func UnionFirstSemigroup[N ~map[K]V, K comparable, V any]() S.Semigroup[N] {
+	return S.MakeSemigroup(func(first N, second N) N {
+		return unionLast(second, first)
 	})
 }

record/monoid.go

@@ -21,6 +21,22 @@ import (
 	S "github.com/IBM/fp-go/semigroup"
 )
 
+// UnionMonoid computes the union of two maps of the same type
 func UnionMonoid[K comparable, V any](s S.Semigroup[V]) M.Monoid[map[K]V] {
 	return G.UnionMonoid[map[K]V](s)
 }
+
+// UnionLastMonoid computes the union of two maps of the same type giving the last map precedence
+func UnionLastMonoid[K comparable, V any]() M.Monoid[map[K]V] {
+	return G.UnionLastMonoid[map[K]V]()
+}
+
+// UnionFirstMonoid computes the union of two maps of the same type giving the first map precedence
+func UnionFirstMonoid[K comparable, V any]() M.Monoid[map[K]V] {
+	return G.UnionFirstMonoid[map[K]V]()
+}
+
+// MergeMonoid computes the union of two maps of the same type giving the last map precedence
+func MergeMonoid[K comparable, V any]() M.Monoid[map[K]V] {
+	return G.UnionLastMonoid[map[K]V]()
+}

record/record.go

@@ -17,27 +17,33 @@ package record
 
 import (
 	Mg "github.com/IBM/fp-go/magma"
+	Mo "github.com/IBM/fp-go/monoid"
 	O "github.com/IBM/fp-go/option"
 	G "github.com/IBM/fp-go/record/generic"
 	T "github.com/IBM/fp-go/tuple"
 )
 
+// IsEmpty tests if a map is empty
 func IsEmpty[K comparable, V any](r map[K]V) bool {
 	return G.IsEmpty(r)
 }
 
+// IsNonEmpty tests if a map is not empty
 func IsNonEmpty[K comparable, V any](r map[K]V) bool {
 	return G.IsNonEmpty(r)
 }
 
+// Keys returns the key in a map
 func Keys[K comparable, V any](r map[K]V) []K {
 	return G.Keys[map[K]V, []K](r)
 }
 
+// Values returns the values in a map
 func Values[K comparable, V any](r map[K]V) []V {
 	return G.Values[map[K]V, []V](r)
 }
 
+// Collect applies a collector function to the key value pairs in a map and returns the result as an array
 func Collect[K comparable, V, R any](f func(K, V) R) func(map[K]V) []R {
 	return G.Collect[map[K]V, []R](f)
 }
@@ -90,10 +96,12 @@ func MapRefWithIndex[K comparable, V, R any](f func(K, *V) R) func(map[K]V) map[
 	return G.MapRefWithIndex[map[K]V, map[K]R](f)
 }
 
+// Lookup returns the entry for a key in a map if it exists
 func Lookup[K comparable, V any](k K) func(map[K]V) O.Option[V] {
 	return G.Lookup[map[K]V](k)
 }
 
+// Has tests if a key is contained in a map
 func Has[K comparable, V any](k K, r map[K]V) bool {
 	return G.Has(k, r)
 }
@@ -102,10 +110,17 @@ func Union[K comparable, V any](m Mg.Magma[V]) func(map[K]V) func(map[K]V) map[K
 	return G.Union[map[K]V](m)
 }
 
+// Merge combines two maps giving the values in the right one precedence. Also refer to [MergeMonoid]
+func Merge[K comparable, V any](right map[K]V) func(map[K]V) map[K]V {
+	return G.Merge[map[K]V](right)
+}
+
+// Empty creates an empty map
 func Empty[K comparable, V any]() map[K]V {
 	return G.Empty[map[K]V]()
 }
 
+// Size returns the number of elements in a map
 func Size[K comparable, V any](r map[K]V) int {
 	return G.Size(r)
 }
@@ -130,6 +145,7 @@ func DeleteAt[K comparable, V any](k K) func(map[K]V) map[K]V {
 	return G.DeleteAt[map[K]V](k)
 }
 
+// Singleton creates a new map with a single entry
 func Singleton[K comparable, V any](k K, v V) map[K]V {
 	return G.Singleton[map[K]V](k, v)
 }
@@ -168,3 +184,34 @@ func IsNonNil[K comparable, V any](m map[K]V) bool {
 func ConstNil[K comparable, V any]() map[K]V {
 	return (map[K]V)(nil)
 }
+
+func MonadChainWithIndex[V1 any, K comparable, V2 any](m Mo.Monoid[map[K]V2], r map[K]V1, f func(K, V1) map[K]V2) map[K]V2 {
+	return G.MonadChainWithIndex(m, r, f)
+}
+
+func MonadChain[V1 any, K comparable, V2 any](m Mo.Monoid[map[K]V2], r map[K]V1, f func(V1) map[K]V2) map[K]V2 {
+	return G.MonadChain(m, r, f)
+}
+
+func ChainWithIndex[V1 any, K comparable, V2 any](m Mo.Monoid[map[K]V2]) func(func(K, V1) map[K]V2) func(map[K]V1) map[K]V2 {
+	return G.ChainWithIndex[map[K]V1](m)
+}
+
+func Chain[V1 any, K comparable, V2 any](m Mo.Monoid[map[K]V2]) func(func(V1) map[K]V2) func(map[K]V1) map[K]V2 {
+	return G.Chain[map[K]V1](m)
+}
+
+// Flatten converts a nested map into a regular map
+func Flatten[K comparable, V any](m Mo.Monoid[map[K]V]) func(map[K]map[K]V) map[K]V {
+	return G.Flatten[map[K]map[K]V](m)
+}
+
+// FilterChainWithIndex creates a new map with only the elements for which the transformation function creates a Some
+func FilterChainWithIndex[V1 any, K comparable, V2 any](m Mo.Monoid[map[K]V2]) func(func(K, V1) O.Option[map[K]V2]) func(map[K]V1) map[K]V2 {
+	return G.FilterChainWithIndex[map[K]V1](m)
+}
+
+// FilterChain creates a new map with only the elements for which the transformation function creates a Some
+func FilterChain[V1 any, K comparable, V2 any](m Mo.Monoid[map[K]V2]) func(func(V1) O.Option[map[K]V2]) func(map[K]V1) map[K]V2 {
+	return G.FilterChain[map[K]V1](m)
+}

record/record_test.go

@@ -16,6 +16,7 @@
 package record
 
 import (
+	"fmt"
 	"sort"
 	"testing"
 
@@ -71,3 +72,30 @@ func TestLookup(t *testing.T) {
 	assert.Equal(t, O.Some("a"), Lookup[string, string]("a")(data))
 	assert.Equal(t, O.None[string](), Lookup[string, string]("a1")(data))
 }
+
+func TestFilterChain(t *testing.T) {
+	src := map[string]int{
+		"a": 1,
+		"b": 2,
+		"c": 3,
+	}
+
+	f := func(k string, value int) O.Option[map[string]string] {
+		if value%2 != 0 {
+			return O.Of(map[string]string{
+				k: fmt.Sprintf("%s%d", k, value),
+			})
+		}
+		return O.None[map[string]string]()
+	}
+
+	// monoid
+	monoid := MergeMonoid[string, string]()
+
+	res := FilterChainWithIndex[int](monoid)(f)(src)
+
+	assert.Equal(t, map[string]string{
+		"a": "a1",
+		"c": "c3",
+	}, res)
+}

record/semigroup.go

@@ -22,3 +22,11 @@ import (
 func UnionSemigroup[K comparable, V any](s S.Semigroup[V]) S.Semigroup[map[K]V] {
 	return G.UnionSemigroup[map[K]V](s)
 }
+
+func UnionLastSemigroup[K comparable, V any]() S.Semigroup[map[K]V] {
+	return G.UnionLastSemigroup[map[K]V]()
+}
+
+func UnionFirstSemigroup[K comparable, V any]() S.Semigroup[map[K]V] {
+	return G.UnionFirstSemigroup[map[K]V]()
+}