fix: implement FoldMap

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

array/array.go

@@ -294,3 +294,13 @@ func SliceRight[A any](start int) func([]A) []A {
 func Copy[A any](b []A) []A {
 	return G.Copy(b)
 }
+
+// FoldMap maps and folds an array. Map the Array passing each value to the iterating function. Then fold the results using the provided Monoid.
+func FoldMap[A, B any](m M.Monoid[B]) func(func(A) B) func([]A) B {
+	return G.FoldMap[[]A](m)
+}
+
+// Fold folds the array using the provided Monoid.
+func Fold[A any](m M.Monoid[A]) func([]A) A {
+	return G.Fold[[]A](m)
+}

array/array_test.go

@@ -173,3 +173,22 @@ func TestFilterMap(t *testing.T) {
 
 	assert.Equal(t, From("a1", "a3"), res)
 }
+
+func TestFoldMap(t *testing.T) {
+	src := From("a", "b", "c")
+
+	fold := FoldMap[string](S.Monoid)(strings.ToUpper)
+
+	assert.Equal(t, "ABC", fold(src))
+}
+
+func ExampleFoldMap() {
+	src := From("a", "b", "c")
+
+	fold := FoldMap[string](S.Monoid)(strings.ToUpper)
+
+	fmt.Println(fold(src))
+
+	// Output: ABC
+
+}

array/generic/array.go

@@ -18,6 +18,7 @@ package generic
 import (
 	F "github.com/IBM/fp-go/function"
 	"github.com/IBM/fp-go/internal/array"
+	M "github.com/IBM/fp-go/monoid"
 	O "github.com/IBM/fp-go/option"
 	"github.com/IBM/fp-go/tuple"
 )
@@ -209,3 +210,19 @@ func Copy[AS ~[]A, A any](b AS) AS {
 	copy(buf, b)
 	return buf
 }
+
+func FoldMap[AS ~[]A, A, B any](m M.Monoid[B]) func(func(A) B) func(AS) B {
+	return func(f func(A) B) func(AS) B {
+		return func(as AS) B {
+			return array.Reduce(as, func(cur B, a A) B {
+				return m.Concat(cur, f(a))
+			}, m.Empty())
+		}
+	}
+}
+
+func Fold[AS ~[]A, A any](m M.Monoid[A]) func(AS) A {
+	return func(as AS) A {
+		return array.Reduce(as, m.Concat, m.Empty())
+	}
+}

array/generic/sort.go

@@ -18,11 +18,17 @@ package generic
 import (
 	"sort"
 
+	F "github.com/IBM/fp-go/function"
 	O "github.com/IBM/fp-go/ord"
 )
 
 // Sort implements a stable sort on the array given the provided ordering
 func Sort[GA ~[]T, T any](ord O.Ord[T]) func(ma GA) GA {
+	return SortByKey[GA](ord, F.Identity[T])
+}
+
+// SortByKey implements a stable sort on the array given the provided ordering on an extracted key
+func SortByKey[GA ~[]T, K, T any](ord O.Ord[K], f func(T) K) func(ma GA) GA {
 
 	return func(ma GA) GA {
 		// nothing to sort
@@ -34,7 +40,7 @@ func Sort[GA ~[]T, T any](ord O.Ord[T]) func(ma GA) GA {
 		cpy := make(GA, l)
 		copy(cpy, ma)
 		sort.Slice(cpy, func(i, j int) bool {
-			return ord.Compare(cpy[i], cpy[j]) < 0
+			return ord.Compare(f(cpy[i]), f(cpy[j])) < 0
 		})
 		return cpy
 	}

array/sort.go

@@ -24,3 +24,8 @@ import (
 func Sort[T any](ord O.Ord[T]) func(ma []T) []T {
 	return G.Sort[[]T](ord)
 }
+
+// SortByKey implements a stable sort on the array given the provided ordering on an extracted key
+func SortByKey[K, T any](ord O.Ord[K], f func(T) K) func(ma []T) []T {
+	return G.SortByKey[[]T](ord, f)
+}

iterator/stateless/generic/iterator.go

@@ -20,6 +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"
+	M "github.com/IBM/fp-go/monoid"
 	N "github.com/IBM/fp-go/number"
 	O "github.com/IBM/fp-go/option"
 	T "github.com/IBM/fp-go/tuple"
@@ -226,3 +227,15 @@ func FilterChain[GVV ~func() O.Option[T.Tuple2[GVV, GV]], GV ~func() O.Option[T.
 		Flatten[GVV],
 	)
 }
+
+func FoldMap[GU ~func() O.Option[T.Tuple2[GU, U]], FCT ~func(U) V, U, V any](m M.Monoid[V]) func(FCT) func(ma GU) V {
+	return func(f FCT) func(ma GU) V {
+		return Reduce[GU](func(cur V, a U) V {
+			return m.Concat(cur, f(a))
+		}, m.Empty())
+	}
+}
+
+func Fold[GU ~func() O.Option[T.Tuple2[GU, U]], U any](m M.Monoid[U]) func(ma GU) U {
+	return Reduce[GU](m.Concat, m.Empty())
+}

iterator/stateless/iterator.go

@@ -18,6 +18,7 @@ package stateless
 import (
 	G "github.com/IBM/fp-go/iterator/stateless/generic"
 	L "github.com/IBM/fp-go/lazy"
+	M "github.com/IBM/fp-go/monoid"
 	O "github.com/IBM/fp-go/option"
 	T "github.com/IBM/fp-go/tuple"
 )
@@ -123,3 +124,13 @@ func Count(start int) Iterator[int] {
 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)
 }
+
+// FoldMap maps and folds an iterator. Map the iterator passing each value to the iterating function. Then fold the results using the provided Monoid.
+func FoldMap[U, V any](m M.Monoid[V]) func(func(U) V) func(ma Iterator[U]) V {
+	return G.FoldMap[Iterator[U], func(U) V, U, V](m)
+}
+
+// Fold folds the iterator using the provided Monoid.
+func Fold[U any](m M.Monoid[U]) func(Iterator[U]) U {
+	return G.Fold[Iterator[U]](m)
+}

iterator/stateless/iterator_test.go

@@ -18,12 +18,14 @@ package stateless
 import (
 	"fmt"
 	"math"
+	"strings"
 	"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"
+	S "github.com/IBM/fp-go/string"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -102,3 +104,14 @@ func TestAp(t *testing.T) {
 
 	assert.Equal(t, A.From("a-1-c", "a-1-d", "a-2-c", "a-2-d", "b-1-c", "b-1-d", "b-2-c", "b-2-d"), it)
 }
+
+func ExampleFoldMap() {
+	src := From("a", "b", "c")
+
+	fold := FoldMap[string](S.Monoid)(strings.ToUpper)
+
+	fmt.Println(fold(src))
+
+	// Output: ABC
+
+}

record/generic/record.go

@@ -16,11 +16,14 @@
 package generic
 
 import (
+	"sort"
+
 	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"
+	"github.com/IBM/fp-go/ord"
 	T "github.com/IBM/fp-go/tuple"
 )
 
@@ -40,6 +43,46 @@ func Values[M ~map[K]V, GV ~[]V, K comparable, V any](r M) GV {
 	return collect[M, GV](r, F.Second[K, V])
 }
 
+func KeysOrd[M ~map[K]V, GK ~[]K, K comparable, V any](o ord.Ord[K]) func(r M) GK {
+	return func(r M) GK {
+		return collectOrd[M, GK](o, r, F.First[K, V])
+	}
+}
+
+func ValuesOrd[M ~map[K]V, GV ~[]V, K comparable, V any](o ord.Ord[K]) func(r M) GV {
+	return func(r M) GV {
+		return collectOrd[M, GV](o, r, F.Second[K, V])
+	}
+}
+
+func collectOrd[M ~map[K]V, GR ~[]R, K comparable, V, R any](o ord.Ord[K], r M, f func(K, V) R) GR {
+	// create the entries
+	entries := toEntriesOrd[M, []T.Tuple2[K, V]](o, r)
+	// collect this array
+	ft := T.Tupled2(f)
+	count := len(entries)
+	result := make(GR, count)
+	for i := count - 1; i >= 0; i-- {
+		result[i] = ft(entries[i])
+	}
+	// done
+	return result
+}
+
+func reduceOrd[M ~map[K]V, K comparable, V, R any](o ord.Ord[K], r M, f func(K, R, V) R, initial R) R {
+	// create the entries
+	entries := toEntriesOrd[M, []T.Tuple2[K, V]](o, r)
+	// collect this array
+	current := initial
+	count := len(entries)
+	for i := 0; i < count; i++ {
+		t := entries[i]
+		current = f(T.First(t), current, T.Second(t))
+	}
+	// done
+	return current
+}
+
 func collect[M ~map[K]V, GR ~[]R, K comparable, V, R any](r M, f func(K, V) R) GR {
 	count := len(r)
 	result := make(GR, count)
@@ -250,6 +293,27 @@ func ToArray[M ~map[K]V, GT ~[]T.Tuple2[K, V], K comparable, V any](r M) GT {
 	return collect[M, GT](r, T.MakeTuple2[K, V])
 }
 
+func toEntriesOrd[M ~map[K]V, GT ~[]T.Tuple2[K, V], K comparable, V any](o ord.Ord[K], r M) GT {
+	// total number of elements
+	count := len(r)
+	// produce an array that we can sort by key
+	entries := make(GT, count)
+	idx := 0
+	for k, v := range r {
+		entries[idx] = T.MakeTuple2(k, v)
+		idx++
+	}
+	sort.Slice(entries, func(i, j int) bool {
+		return o.Compare(T.First(entries[i]), T.First(entries[j])) < 0
+	})
+	// final entries
+	return entries
+}
+
+func ToEntriesOrd[M ~map[K]V, GT ~[]T.Tuple2[K, V], K comparable, V any](o ord.Ord[K]) func(r M) GT {
+	return F.Bind1st(toEntriesOrd[M, GT, K, V], o)
+}
+
 func ToEntries[M ~map[K]V, GT ~[]T.Tuple2[K, V], K comparable, V any](r M) GT {
 	return ToArray[M, GT](r)
 }
@@ -379,3 +443,67 @@ func IsNonNil[M ~map[K]V, K comparable, V any](m M) bool {
 func ConstNil[M ~map[K]V, K comparable, V any]() M {
 	return (M)(nil)
 }
+
+func FoldMap[AS ~map[K]A, K comparable, A, B any](m Mo.Monoid[B]) func(func(A) B) func(AS) B {
+	return func(f func(A) B) func(AS) B {
+		return Reduce[AS](func(cur B, a A) B {
+			return m.Concat(cur, f(a))
+		}, m.Empty())
+	}
+}
+
+func Fold[AS ~map[K]A, K comparable, A any](m Mo.Monoid[A]) func(AS) A {
+	return Reduce[AS](m.Concat, m.Empty())
+}
+
+func FoldMapWithIndex[AS ~map[K]A, K comparable, A, B any](m Mo.Monoid[B]) func(func(K, A) B) func(AS) B {
+	return func(f func(K, A) B) func(AS) B {
+		return ReduceWithIndex[AS](func(k K, cur B, a A) B {
+			return m.Concat(cur, f(k, a))
+		}, m.Empty())
+	}
+}
+
+func ReduceOrdWithIndex[M ~map[K]V, K comparable, V, R any](o ord.Ord[K]) func(func(K, R, V) R, R) func(M) R {
+	return func(f func(K, R, V) R, initial R) func(M) R {
+		return func(m M) R {
+			return reduceOrd(o, m, f, initial)
+		}
+	}
+}
+
+func ReduceOrd[M ~map[K]V, K comparable, V, R any](o ord.Ord[K]) func(func(R, V) R, R) func(M) R {
+	ro := ReduceOrdWithIndex[M, K, V, R](o)
+	return func(f func(R, V) R, initial R) func(M) R {
+		return ro(F.Ignore1of3[K](f), initial)
+	}
+}
+
+func FoldMapOrd[AS ~map[K]A, K comparable, A, B any](o ord.Ord[K]) func(m Mo.Monoid[B]) func(func(A) B) func(AS) B {
+	red := ReduceOrd[AS, K, A, B](o)
+	return func(m Mo.Monoid[B]) func(func(A) B) func(AS) B {
+		return func(f func(A) B) func(AS) B {
+			return red(func(cur B, a A) B {
+				return m.Concat(cur, f(a))
+			}, m.Empty())
+		}
+	}
+}
+
+func FoldOrd[AS ~map[K]A, K comparable, A any](o ord.Ord[K]) func(m Mo.Monoid[A]) func(AS) A {
+	red := ReduceOrd[AS, K, A, A](o)
+	return func(m Mo.Monoid[A]) func(AS) A {
+		return red(m.Concat, m.Empty())
+	}
+}
+
+func FoldMapOrdWithIndex[AS ~map[K]A, K comparable, A, B any](o ord.Ord[K]) func(m Mo.Monoid[B]) func(func(K, A) B) func(AS) B {
+	red := ReduceOrdWithIndex[AS, K, A, B](o)
+	return func(m Mo.Monoid[B]) func(func(K, A) B) func(AS) B {
+		return func(f func(K, A) B) func(AS) B {
+			return red(func(k K, cur B, a A) B {
+				return m.Concat(cur, f(k, a))
+			}, m.Empty())
+		}
+	}
+}

record/record.go

@@ -19,6 +19,7 @@ import (
 	Mg "github.com/IBM/fp-go/magma"
 	Mo "github.com/IBM/fp-go/monoid"
 	O "github.com/IBM/fp-go/option"
+	"github.com/IBM/fp-go/ord"
 	G "github.com/IBM/fp-go/record/generic"
 	T "github.com/IBM/fp-go/tuple"
 )
@@ -215,3 +216,53 @@ func FilterChainWithIndex[V1 any, K comparable, V2 any](m Mo.Monoid[map[K]V2]) f
 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)
 }
+
+// FoldMap maps and folds a record. Map the record passing each value to the iterating function. Then fold the results using the provided Monoid.
+func FoldMap[K comparable, A, B any](m Mo.Monoid[B]) func(func(A) B) func(map[K]A) B {
+	return G.FoldMap[map[K]A](m)
+}
+
+// FoldMapWithIndex maps and folds a record. Map the record passing each value to the iterating function. Then fold the results using the provided Monoid.
+func FoldMapWithIndex[K comparable, A, B any](m Mo.Monoid[B]) func(func(K, A) B) func(map[K]A) B {
+	return G.FoldMapWithIndex[map[K]A](m)
+}
+
+// Fold folds the record using the provided Monoid.
+func Fold[K comparable, A any](m Mo.Monoid[A]) func(map[K]A) A {
+	return G.Fold[map[K]A](m)
+}
+
+// ReduceOrdWithIndex reduces a map into a single value via a reducer function making sure that the keys are passed to the reducer in the specified order
+func ReduceOrdWithIndex[V, R any, K comparable](o ord.Ord[K]) func(func(K, R, V) R, R) func(map[K]V) R {
+	return G.ReduceOrdWithIndex[map[K]V, K, V, R](o)
+}
+
+// ReduceOrd reduces a map into a single value via a reducer function making sure that the keys are passed to the reducer in the specified order
+func ReduceOrd[V, R any, K comparable](o ord.Ord[K]) func(func(R, V) R, R) func(map[K]V) R {
+	return G.ReduceOrd[map[K]V, K, V, R](o)
+}
+
+// FoldMap maps and folds a record. Map the record passing each value to the iterating function. Then fold the results using the provided Monoid and the items in the provided order
+func FoldMapOrd[A, B any, K comparable](o ord.Ord[K]) func(m Mo.Monoid[B]) func(func(A) B) func(map[K]A) B {
+	return G.FoldMapOrd[map[K]A, K, A, B](o)
+}
+
+// Fold folds the record using the provided Monoid with the items passed in the given order
+func FoldOrd[A any, K comparable](o ord.Ord[K]) func(m Mo.Monoid[A]) func(map[K]A) A {
+	return G.FoldOrd[map[K]A, K, A](o)
+}
+
+// FoldMapWithIndex maps and folds a record. Map the record passing each value to the iterating function. Then fold the results using the provided Monoid and the items in the provided order
+func FoldMapOrdWithIndex[K comparable, A, B any](o ord.Ord[K]) func(m Mo.Monoid[B]) func(func(K, A) B) func(map[K]A) B {
+	return G.FoldMapOrdWithIndex[map[K]A, K, A, B](o)
+}
+
+// KeysOrd returns the keys in the map in their given order
+func KeysOrd[V any, K comparable](o ord.Ord[K]) func(r map[K]V) []K {
+	return G.KeysOrd[map[K]V, []K, K, V](o)
+}
+
+// ValuesOrd returns the values in the map ordered by their keys in the given order
+func ValuesOrd[V any, K comparable](o ord.Ord[K]) func(r map[K]V) []V {
+	return G.ValuesOrd[map[K]V, []V, K, V](o)
+}

record/record_test.go

@@ -18,10 +18,12 @@ package record
 import (
 	"fmt"
 	"sort"
+	"strings"
 	"testing"
 
 	"github.com/IBM/fp-go/internal/utils"
 	O "github.com/IBM/fp-go/option"
+	S "github.com/IBM/fp-go/string"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -99,3 +101,33 @@ func TestFilterChain(t *testing.T) {
 		"c": "c3",
 	}, res)
 }
+
+func ExampleFoldMap() {
+	src := map[string]string{
+		"a": "a",
+		"b": "b",
+		"c": "c",
+	}
+
+	fold := FoldMap[string, string](S.Monoid)(strings.ToUpper)
+
+	fmt.Println(fold(src))
+
+	// Output: ABC
+
+}
+
+func ExampleValuesOrd() {
+	src := map[string]string{
+		"c": "a",
+		"b": "b",
+		"a": "c",
+	}
+
+	getValues := ValuesOrd[string](S.Ord)
+
+	fmt.Println(getValues(src))
+
+	// Output: [c b a]
+
+}