fix: overhaul record

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

v2/README.md

@@ -452,17 +452,27 @@ func process() IOResult[string] {
 
 ### Core Modules
 
+#### Standard Packages (Struct-based)
 - **Option** - Represent optional values without nil
 - **Either** - Type-safe error handling with left/right values
-- **Result** - Simplified Either with error as left type
+- **Result** - Simplified Either with error as left type (recommended for error handling)
 - **IO** - Lazy evaluation and side effect management
-- **IOEither** - Combine IO with error handling
+- **IOResult** - Combine IO with Result for error handling (recommended over IOEither)
 - **Reader** - Dependency injection pattern
-- **ReaderIOEither** - Combine Reader, IO, and Either for complex workflows
+- **ReaderIOResult** - Combine Reader, IO, and Result for complex workflows
 - **Array** - Functional array operations
 - **Record** - Functional record/map operations
 - **Optics** - Lens, Prism, Optional, and Traversal for immutable updates
 
+#### Idiomatic Packages (Tuple-based, High Performance)
+- **idiomatic/option** - Option monad using native Go `(value, bool)` tuples
+- **idiomatic/result** - Result monad using native Go `(value, error)` tuples
+- **idiomatic/ioresult** - IOResult monad using `func() (value, error)` for IO operations
+- **idiomatic/readerresult** - Reader monad combined with Result pattern
+- **idiomatic/readerioresult** - Reader monad combined with IOResult pattern
+
+The idiomatic packages offer 2-10x performance improvements and zero allocations by using Go's native tuple patterns instead of struct wrappers. Use them for performance-critical code or when you prefer Go's native error handling style.
+
 ## 🤔 Should I Migrate?
 
 **Migrate to V2 if:**

v2/di/erasure/injector.go

@@ -23,14 +23,15 @@ import (
 	IOR "github.com/IBM/fp-go/v2/ioresult"
 	L "github.com/IBM/fp-go/v2/lazy"
 	O "github.com/IBM/fp-go/v2/option"
+	"github.com/IBM/fp-go/v2/pair"
 	R "github.com/IBM/fp-go/v2/record"
 	T "github.com/IBM/fp-go/v2/tuple"
 
 	"sync"
 )
 
-func providerToEntry(p Provider) T.Tuple2[string, ProviderFactory] {
-	return T.MakeTuple2(p.Provides().Id(), p.Factory())
+func providerToEntry(p Provider) Entry[string, ProviderFactory] {
+	return pair.MakePair(p.Provides().Id(), p.Factory())
 }
 
 func itemProviderToMap(p Provider) map[string][]ProviderFactory {

v2/di/erasure/types.go

@@ -4,10 +4,12 @@ import (
 	"github.com/IBM/fp-go/v2/iooption"
 	"github.com/IBM/fp-go/v2/ioresult"
 	"github.com/IBM/fp-go/v2/option"
+	"github.com/IBM/fp-go/v2/record"
 )
 
 type (
 	Option[T any]              = option.Option[T]
 	IOResult[T any]            = ioresult.IOResult[T]
 	IOOption[T any]            = iooption.IOOption[T]
+	Entry[K comparable, V any] = record.Entry[K, V]
 )

v2/di/types.go

@@ -4,6 +4,7 @@ import (
 	"github.com/IBM/fp-go/v2/context/ioresult"
 	"github.com/IBM/fp-go/v2/iooption"
 	"github.com/IBM/fp-go/v2/option"
+	"github.com/IBM/fp-go/v2/record"
 	"github.com/IBM/fp-go/v2/result"
 )
 
@@ -12,4 +13,5 @@ type (
 	Result[T any]              = result.Result[T]
 	IOResult[T any]            = ioresult.IOResult[T]
 	IOOption[T any]            = iooption.IOOption[T]
+	Entry[K comparable, V any] = record.Entry[K, V]
 )

v2/iterator/iter/iter_test.go

@@ -22,9 +22,11 @@ import (
 	"strings"
 	"testing"
 
+	A "github.com/IBM/fp-go/v2/array"
 	F "github.com/IBM/fp-go/v2/function"
 	N "github.com/IBM/fp-go/v2/number"
 	O "github.com/IBM/fp-go/v2/option"
+	R "github.com/IBM/fp-go/v2/record"
 	S "github.com/IBM/fp-go/v2/string"
 	"github.com/stretchr/testify/assert"
 )
@@ -42,13 +44,13 @@ func toMap[K comparable, V any](seq Seq2[K, V]) map[K]V {
 func TestOf(t *testing.T) {
 	seq := Of(42)
 	result := toSlice(seq)
-	assert.Equal(t, []int{42}, result)
+	assert.Equal(t, A.Of(42), result)
 }
 
 func TestOf2(t *testing.T) {
 	seq := Of2("key", 100)
 	result := toMap(seq)
-	assert.Equal(t, map[string]int{"key": 100}, result)
+	assert.Equal(t, R.Of("key", 100), result)
 }
 
 func TestFrom(t *testing.T) {
@@ -587,3 +589,29 @@ func ExampleMonoid() {
 	fmt.Println(result)
 	// Output: [1 2 3 4 5 6]
 }
+
+func TestMonadMapToArray(t *testing.T) {
+	seq := From(1, 2, 3)
+	result := MonadMapToArray(seq, N.Mul(2))
+	assert.Equal(t, []int{2, 4, 6}, result)
+}
+
+func TestMonadMapToArrayEmpty(t *testing.T) {
+	seq := Empty[int]()
+	result := MonadMapToArray(seq, N.Mul(2))
+	assert.Empty(t, result)
+}
+
+func TestMapToArray(t *testing.T) {
+	seq := From(1, 2, 3)
+	mapper := MapToArray(N.Mul(2))
+	result := mapper(seq)
+	assert.Equal(t, []int{2, 4, 6}, result)
+}
+
+func TestMapToArrayIdentity(t *testing.T) {
+	seq := From("a", "b", "c")
+	mapper := MapToArray(F.Identity[string])
+	result := mapper(seq)
+	assert.Equal(t, []string{"a", "b", "c"}, result)
+}

v2/record/coverage.out

@@ -0,0 +1,85 @@
+mode: set
+github.com/IBM/fp-go/v2/record/bind.go:33.40,35.2 1 0
+github.com/IBM/fp-go/v2/record/bind.go:71.144,73.2 1 0
+github.com/IBM/fp-go/v2/record/bind.go:79.27,81.2 1 0
+github.com/IBM/fp-go/v2/record/bind.go:87.27,89.2 1 0
+github.com/IBM/fp-go/v2/record/bind.go:92.80,94.2 1 0
+github.com/IBM/fp-go/v2/record/bind.go:129.135,131.2 1 0
+github.com/IBM/fp-go/v2/record/eq.go:23.55,25.2 1 0
+github.com/IBM/fp-go/v2/record/eq.go:28.56,30.2 1 1
+github.com/IBM/fp-go/v2/record/monoid.go:25.75,27.2 1 1
+github.com/IBM/fp-go/v2/record/monoid.go:30.63,32.2 1 1
+github.com/IBM/fp-go/v2/record/monoid.go:35.64,37.2 1 1
+github.com/IBM/fp-go/v2/record/monoid.go:40.59,42.2 1 1
+github.com/IBM/fp-go/v2/record/record.go:28.51,30.2 1 1
+github.com/IBM/fp-go/v2/record/record.go:33.54,35.2 1 1
+github.com/IBM/fp-go/v2/record/record.go:38.47,40.2 1 1
+github.com/IBM/fp-go/v2/record/record.go:43.49,45.2 1 1
+github.com/IBM/fp-go/v2/record/record.go:48.72,50.2 1 1
+github.com/IBM/fp-go/v2/record/record.go:53.92,55.2 1 1
+github.com/IBM/fp-go/v2/record/record.go:57.80,59.2 1 1
+github.com/IBM/fp-go/v2/record/record.go:61.92,63.2 1 1
+github.com/IBM/fp-go/v2/record/record.go:65.84,67.2 1 1
+github.com/IBM/fp-go/v2/record/record.go:69.96,71.2 1 1
+github.com/IBM/fp-go/v2/record/record.go:73.71,75.2 1 1
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+github.com/IBM/fp-go/v2/record/record.go:284.74,286.2 1 1
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+github.com/IBM/fp-go/v2/record/record.go:294.80,296.2 1 1
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+github.com/IBM/fp-go/v2/record/record.go:314.73,316.2 1 1
+github.com/IBM/fp-go/v2/record/record.go:324.60,326.2 1 0
+github.com/IBM/fp-go/v2/record/record.go:332.55,334.2 1 1
+github.com/IBM/fp-go/v2/record/record.go:336.105,338.2 1 1
+github.com/IBM/fp-go/v2/record/record.go:340.106,342.2 1 1
+github.com/IBM/fp-go/v2/record/record.go:344.48,346.2 1 1
+github.com/IBM/fp-go/v2/record/semigroup.go:53.81,55.2 1 1
+github.com/IBM/fp-go/v2/record/semigroup.go:80.69,82.2 1 1
+github.com/IBM/fp-go/v2/record/semigroup.go:107.70,109.2 1 1
+github.com/IBM/fp-go/v2/record/traverse.go:27.41,29.2 1 1
+github.com/IBM/fp-go/v2/record/traverse.go:39.38,41.2 1 1
+github.com/IBM/fp-go/v2/record/traverse.go:50.23,53.2 1 1

v2/record/generic/record.go

@@ -26,7 +26,7 @@ import (
 	Mo "github.com/IBM/fp-go/v2/monoid"
 	O "github.com/IBM/fp-go/v2/option"
 	"github.com/IBM/fp-go/v2/ord"
-	T "github.com/IBM/fp-go/v2/tuple"
+	"github.com/IBM/fp-go/v2/pair"
 )
 
 func IsEmpty[M ~map[K]V, K comparable, V any](r M) bool {
@@ -59,9 +59,9 @@ func ValuesOrd[M ~map[K]V, GV ~[]V, K comparable, V any](o ord.Ord[K]) func(r M)
 
 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)
+	entries := toEntriesOrd[M, []pair.Pair[K, V]](o, r)
 	// collect this array
-	ft := T.Tupled2(f)
+	ft := pair.Paired(f)
 	count := len(entries)
 	result := make(GR, count)
 	for i := count - 1; i >= 0; i-- {
@@ -73,13 +73,13 @@ func collectOrd[M ~map[K]V, GR ~[]R, K comparable, V, R any](o ord.Ord[K], r M,
 
 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)
+	entries := toEntriesOrd[M, []pair.Pair[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))
+		current = f(pair.Head(t), current, pair.Tail(t))
 	}
 	// done
 	return current
@@ -318,32 +318,32 @@ func Size[M ~map[K]V, K comparable, V any](r M) int {
 	return len(r)
 }
 
-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 ToArray[M ~map[K]V, GT ~[]pair.Pair[K, V], K comparable, V any](r M) GT {
+	return collect[M, GT](r, pair.MakePair[K, V])
 }
 
-func toEntriesOrd[M ~map[K]V, GT ~[]T.Tuple2[K, V], K comparable, V any](o ord.Ord[K], r M) GT {
+func toEntriesOrd[M ~map[K]V, GT ~[]pair.Pair[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)
+		entries[idx] = pair.MakePair(k, v)
 		idx++
 	}
 	sort.Slice(entries, func(i, j int) bool {
-		return o.Compare(T.First(entries[i]), T.First(entries[j])) < 0
+		return o.Compare(pair.Head(entries[i]), pair.Head(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 {
+func ToEntriesOrd[M ~map[K]V, GT ~[]pair.Pair[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 {
+func ToEntries[M ~map[K]V, GT ~[]pair.Pair[K, V], K comparable, V any](r M) GT {
 	return ToArray[M, GT](r)
 }
 
@@ -351,7 +351,7 @@ func ToEntries[M ~map[K]V, GT ~[]T.Tuple2[K, V], K comparable, V any](r M) GT {
 // its values into a tuple. The key and value are then used to populate the map. Duplicate
 // values are resolved via the provided [Mg.Magma]
 func FromFoldableMap[
-	FCT ~func(A) T.Tuple2[K, V],
+	FCT ~func(A) pair.Pair[K, V],
 	HKTA any,
 	FOLDABLE ~func(func(M, A) M, M) func(HKTA) M,
 	M ~map[K]V,
@@ -364,12 +364,12 @@ func FromFoldableMap[
 				dst = make(M)
 			}
 			e := f(a)
-			k := T.First(e)
+			k := pair.Head(e)
 			old, ok := dst[k]
 			if ok {
-				dst[k] = m.Concat(old, T.Second(e))
+				dst[k] = m.Concat(old, pair.Tail(e))
 			} else {
-				dst[k] = T.Second(e)
+				dst[k] = pair.Tail(e)
 			}
 			return dst
 		}, Empty[M]())
@@ -378,15 +378,15 @@ func FromFoldableMap[
 
 func FromFoldable[
 	HKTA any,
-	FOLDABLE ~func(func(M, T.Tuple2[K, V]) M, M) func(HKTA) M,
+	FOLDABLE ~func(func(M, pair.Pair[K, V]) M, M) func(HKTA) M,
 	M ~map[K]V,
 	K comparable,
 	V any](m Mg.Magma[V], red FOLDABLE) func(fa HKTA) M {
-	return FromFoldableMap[func(T.Tuple2[K, V]) T.Tuple2[K, V]](m, red)(F.Identity[T.Tuple2[K, V]])
+	return FromFoldableMap[func(pair.Pair[K, V]) pair.Pair[K, V]](m, red)(F.Identity[pair.Pair[K, V]])
 }
 
 func FromArrayMap[
-	FCT ~func(A) T.Tuple2[K, V],
+	FCT ~func(A) pair.Pair[K, V],
 	GA ~[]A,
 	M ~map[K]V,
 	A any,
@@ -396,17 +396,17 @@ func FromArrayMap[
 }
 
 func FromArray[
-	GA ~[]T.Tuple2[K, V],
+	GA ~[]pair.Pair[K, V],
 	M ~map[K]V,
 	K comparable,
 	V any](m Mg.Magma[V]) func(fa GA) M {
-	return FromFoldable(m, F.Bind23of3(RAG.Reduce[GA, T.Tuple2[K, V], M]))
+	return FromFoldable(m, F.Bind23of3(RAG.Reduce[GA, pair.Pair[K, V], M]))
 }
 
-func FromEntries[M ~map[K]V, GT ~[]T.Tuple2[K, V], K comparable, V any](fa GT) M {
+func FromEntries[M ~map[K]V, GT ~[]pair.Pair[K, V], K comparable, V any](fa GT) M {
 	m := make(M)
 	for _, t := range fa {
-		upsertAtReadWrite(m, t.F1, t.F2)
+		upsertAtReadWrite(m, pair.Head(t), pair.Tail(t))
 	}
 	return m
 }

v2/record/record.go

@@ -22,7 +22,6 @@ import (
 	O "github.com/IBM/fp-go/v2/option"
 	"github.com/IBM/fp-go/v2/ord"
 	G "github.com/IBM/fp-go/v2/record/generic"
-	T "github.com/IBM/fp-go/v2/tuple"
 )
 
 // IsEmpty tests if a map is empty
@@ -55,51 +54,63 @@ func CollectOrd[V, R any, K comparable](o ord.Ord[K]) func(func(K, V) R) func(ma
 	return G.CollectOrd[map[K]V, []R](o)
 }
 
+// Reduce reduces a map to a single value by applying a reducer function to each value
 func Reduce[K comparable, V, R any](f func(R, V) R, initial R) func(map[K]V) R {
 	return G.Reduce[map[K]V](f, initial)
 }
 
+// ReduceWithIndex reduces a map to a single value by applying a reducer function to each key-value pair
 func ReduceWithIndex[K comparable, V, R any](f func(K, R, V) R, initial R) func(map[K]V) R {
 	return G.ReduceWithIndex[map[K]V](f, initial)
 }
 
+// ReduceRef reduces a map to a single value by applying a reducer function to each value reference
 func ReduceRef[K comparable, V, R any](f func(R, *V) R, initial R) func(map[K]V) R {
 	return G.ReduceRef[map[K]V](f, initial)
 }
 
+// ReduceRefWithIndex reduces a map to a single value by applying a reducer function to each key-value pair with value references
 func ReduceRefWithIndex[K comparable, V, R any](f func(K, R, *V) R, initial R) func(map[K]V) R {
 	return G.ReduceRefWithIndex[map[K]V](f, initial)
 }
 
+// MonadMap transforms each value in a map using the provided function
 func MonadMap[K comparable, V, R any](r map[K]V, f func(V) R) map[K]R {
 	return G.MonadMap[map[K]V, map[K]R](r, f)
 }
 
+// MonadMapWithIndex transforms each key-value pair in a map using the provided function
 func MonadMapWithIndex[K comparable, V, R any](r map[K]V, f func(K, V) R) map[K]R {
 	return G.MonadMapWithIndex[map[K]V, map[K]R](r, f)
 }
 
+// MonadMapRefWithIndex transforms each key-value pair in a map using the provided function with value references
 func MonadMapRefWithIndex[K comparable, V, R any](r map[K]V, f func(K, *V) R) map[K]R {
 	return G.MonadMapRefWithIndex[map[K]V, map[K]R](r, f)
 }
 
+// MonadMapRef transforms each value in a map using the provided function with value references
 func MonadMapRef[K comparable, V, R any](r map[K]V, f func(*V) R) map[K]R {
 	return G.MonadMapRef[map[K]V, map[K]R](r, f)
 }
 
-func Map[K comparable, V, R any](f func(V) R) func(map[K]V) map[K]R {
+// Map returns a function that transforms each value in a map using the provided function
+func Map[K comparable, V, R any](f func(V) R) Operator[K, V, R] {
 	return G.Map[map[K]V, map[K]R](f)
 }
 
-func MapRef[K comparable, V, R any](f func(*V) R) func(map[K]V) map[K]R {
+// MapRef returns a function that transforms each value in a map using the provided function with value references
+func MapRef[K comparable, V, R any](f func(*V) R) Operator[K, V, R] {
 	return G.MapRef[map[K]V, map[K]R](f)
 }
 
-func MapWithIndex[K comparable, V, R any](f func(K, V) R) func(map[K]V) map[K]R {
+// MapWithIndex returns a function that transforms each key-value pair in a map using the provided function
+func MapWithIndex[K comparable, V, R any](f func(K, V) R) Operator[K, V, R] {
 	return G.MapWithIndex[map[K]V, map[K]R](f)
 }
 
-func MapRefWithIndex[K comparable, V, R any](f func(K, *V) R) func(map[K]V) map[K]R {
+// MapRefWithIndex returns a function that transforms each key-value pair in a map using the provided function with value references
+func MapRefWithIndex[K comparable, V, R any](f func(K, *V) R) Operator[K, V, R] {
 	return G.MapRefWithIndex[map[K]V, map[K]R](f)
 }
 
@@ -118,12 +129,13 @@ func Has[K comparable, V any](k K, r map[K]V) bool {
 	return G.Has(k, r)
 }
 
-func Union[K comparable, V any](m Mg.Magma[V]) func(map[K]V) func(map[K]V) map[K]V {
+// Union combines two maps using the provided Magma to resolve conflicts for duplicate keys
+func Union[K comparable, V any](m Mg.Magma[V]) func(map[K]V) Operator[K, V, V] {
 	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 {
+func Merge[K comparable, V any](right map[K]V) Operator[K, V, V] {
 	return G.Merge(right)
 }
 
@@ -137,23 +149,28 @@ func Size[K comparable, V any](r map[K]V) int {
 	return G.Size(r)
 }
 
-func ToArray[K comparable, V any](r map[K]V) []T.Tuple2[K, V] {
-	return G.ToArray[map[K]V, []T.Tuple2[K, V]](r)
+// ToArray converts a map to an array of key-value pairs
+func ToArray[K comparable, V any](r map[K]V) Entries[K, V] {
+	return G.ToArray[map[K]V, Entries[K, V]](r)
 }
 
-func ToEntries[K comparable, V any](r map[K]V) []T.Tuple2[K, V] {
-	return G.ToEntries[map[K]V, []T.Tuple2[K, V]](r)
+// ToEntries converts a map to an array of key-value pairs (alias for ToArray)
+func ToEntries[K comparable, V any](r map[K]V) Entries[K, V] {
+	return G.ToEntries[map[K]V, Entries[K, V]](r)
 }
 
-func FromEntries[K comparable, V any](fa []T.Tuple2[K, V]) map[K]V {
+// FromEntries creates a map from an array of key-value pairs
+func FromEntries[K comparable, V any](fa Entries[K, V]) map[K]V {
 	return G.FromEntries[map[K]V](fa)
 }
 
-func UpsertAt[K comparable, V any](k K, v V) func(map[K]V) map[K]V {
+// UpsertAt returns a function that inserts or updates a key-value pair in a map
+func UpsertAt[K comparable, V any](k K, v V) Operator[K, V, V] {
 	return G.UpsertAt[map[K]V](k, v)
 }
 
-func DeleteAt[K comparable, V any](k K) func(map[K]V) map[K]V {
+// DeleteAt returns a function that removes a key from a map
+func DeleteAt[K comparable, V any](k K) Operator[K, V, V] {
 	return G.DeleteAt[map[K]V](k)
 }
 
@@ -163,22 +180,22 @@ func Singleton[K comparable, V any](k K, v V) map[K]V {
 }
 
 // FilterMapWithIndex creates a new map with only the elements for which the transformation function creates a Some
-func FilterMapWithIndex[K comparable, V1, V2 any](f func(K, V1) O.Option[V2]) func(map[K]V1) map[K]V2 {
+func FilterMapWithIndex[K comparable, V1, V2 any](f func(K, V1) O.Option[V2]) Operator[K, V1, V2] {
 	return G.FilterMapWithIndex[map[K]V1, map[K]V2](f)
 }
 
 // FilterMap creates a new map with only the elements for which the transformation function creates a Some
-func FilterMap[K comparable, V1, V2 any](f func(V1) O.Option[V2]) func(map[K]V1) map[K]V2 {
+func FilterMap[K comparable, V1, V2 any](f func(V1) O.Option[V2]) Operator[K, V1, V2] {
 	return G.FilterMap[map[K]V1, map[K]V2](f)
 }
 
 // Filter creates a new map with only the elements that match the predicate
-func Filter[K comparable, V any](f func(K) bool) func(map[K]V) map[K]V {
+func Filter[K comparable, V any](f func(K) bool) Operator[K, V, V] {
 	return G.Filter[map[K]V](f)
 }
 
 // FilterWithIndex creates a new map with only the elements that match the predicate
-func FilterWithIndex[K comparable, V any](f func(K, V) bool) func(map[K]V) map[K]V {
+func FilterWithIndex[K comparable, V any](f func(K, V) bool) Operator[K, V, V] {
 	return G.FilterWithIndex[map[K]V](f)
 }
 
@@ -197,19 +214,23 @@ func ConstNil[K comparable, V any]() map[K]V {
 	return map[K]V(nil)
 }
 
+// MonadChainWithIndex chains a map transformation function that produces maps, combining results using the provided Monoid
 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)
 }
 
+// MonadChain chains a map transformation function that produces maps, combining results using the provided Monoid
 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 {
+// ChainWithIndex returns a function that chains a map transformation function that produces maps, combining results using the provided Monoid
+func ChainWithIndex[V1 any, K comparable, V2 any](m Mo.Monoid[map[K]V2]) func(func(K, V1) map[K]V2) Operator[K, V1, 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 {
+// Chain returns a function that chains a map transformation function that produces maps, combining results using the provided Monoid
+func Chain[V1 any, K comparable, V2 any](m Mo.Monoid[map[K]V2]) func(func(V1) map[K]V2) Operator[K, V1, V2] {
 	return G.Chain[map[K]V1](m)
 }
 
@@ -219,12 +240,12 @@ func Flatten[K comparable, V any](m Mo.Monoid[map[K]V]) func(map[K]map[K]V) map[
 }
 
 // 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 {
+func FilterChainWithIndex[V1 any, K comparable, V2 any](m Mo.Monoid[map[K]V2]) func(func(K, V1) O.Option[map[K]V2]) Operator[K, V1, 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 {
+func FilterChain[V1 any, K comparable, V2 any](m Mo.Monoid[map[K]V2]) func(func(V1) O.Option[map[K]V2]) Operator[K, V1, V2] {
 	return G.FilterChain[map[K]V1](m)
 }
 
@@ -278,10 +299,12 @@ func ValuesOrd[V any, K comparable](o ord.Ord[K]) func(r map[K]V) []V {
 	return G.ValuesOrd[map[K]V, []V](o)
 }
 
+// MonadFlap applies a value to a map of functions, producing a map of results
 func MonadFlap[B any, K comparable, A any](fab map[K]func(A) B, a A) map[K]B {
 	return G.MonadFlap[map[K]func(A) B, map[K]B](fab, a)
 }
 
+// Flap returns a function that applies a value to a map of functions, producing a map of results
 func Flap[B any, K comparable, A any](a A) func(map[K]func(A) B) map[K]B {
 	return G.Flap[map[K]func(A) B, map[K]B](a)
 }
@@ -303,8 +326,8 @@ func FromFoldableMap[
 	A any,
 	HKTA any,
 	K comparable,
-	V any](m Mg.Magma[V], red FOLDABLE) func(f func(A) T.Tuple2[K, V]) func(fa HKTA) map[K]V {
-	return G.FromFoldableMap[func(A) T.Tuple2[K, V]](m, red)
+	V any](m Mg.Magma[V], red FOLDABLE) func(f func(A) Entry[K, V]) func(fa HKTA) map[K]V {
+	return G.FromFoldableMap[func(A) Entry[K, V]](m, red)
 }
 
 // FromArrayMap converts from an array to a map
@@ -312,15 +335,15 @@ func FromFoldableMap[
 func FromArrayMap[
 	A any,
 	K comparable,
-	V any](m Mg.Magma[V]) func(f func(A) T.Tuple2[K, V]) func(fa []A) map[K]V {
-	return G.FromArrayMap[func(A) T.Tuple2[K, V], []A, map[K]V](m)
+	V any](m Mg.Magma[V]) func(f func(A) Entry[K, V]) func(fa []A) map[K]V {
+	return G.FromArrayMap[func(A) Entry[K, V], []A, map[K]V](m)
 }
 
 // FromFoldable converts from a reducer to a map
 // Duplicate keys are resolved by the provided [Mg.Magma]
 func FromFoldable[
 	HKTA any,
-	FOLDABLE ~func(func(map[K]V, T.Tuple2[K, V]) map[K]V, map[K]V) func(HKTA) map[K]V, // the reduce function
+	FOLDABLE ~func(func(map[K]V, Entry[K, V]) map[K]V, map[K]V) func(HKTA) map[K]V, // the reduce function
 	K comparable,
 	V any](m Mg.Magma[V], red FOLDABLE) func(fa HKTA) map[K]V {
 	return G.FromFoldable(m, red)
@@ -330,14 +353,21 @@ func FromFoldable[
 // Duplicate keys are resolved by the provided [Mg.Magma]
 func FromArray[
 	K comparable,
-	V any](m Mg.Magma[V]) func(fa []T.Tuple2[K, V]) map[K]V {
-	return G.FromArray[[]T.Tuple2[K, V], map[K]V](m)
+	V any](m Mg.Magma[V]) func(fa Entries[K, V]) map[K]V {
+	return G.FromArray[Entries[K, V], map[K]V](m)
 }
 
+// MonadAp applies a map of functions to a map of values, combining results using the provided Monoid
 func MonadAp[A any, K comparable, B any](m Mo.Monoid[map[K]B], fab map[K]func(A) B, fa map[K]A) map[K]B {
 	return G.MonadAp(m, fab, fa)
 }
 
+// Ap returns a function that applies a map of functions to a map of values, combining results using the provided Monoid
 func Ap[A any, K comparable, B any](m Mo.Monoid[map[K]B]) func(fa map[K]A) func(map[K]func(A) B) map[K]B {
 	return G.Ap[map[K]B, map[K]func(A) B, map[K]A](m)
 }
+
+// Of creates a map with a single key-value pair
+func Of[K comparable, A any](k K, a A) map[K]A {
+	return map[K]A{k: a}
+}

v2/record/record_test.go

@@ -25,8 +25,8 @@ import (
 	"github.com/IBM/fp-go/v2/internal/utils"
 	Mg "github.com/IBM/fp-go/v2/magma"
 	O "github.com/IBM/fp-go/v2/option"
+	P "github.com/IBM/fp-go/v2/pair"
 	S "github.com/IBM/fp-go/v2/string"
-	T "github.com/IBM/fp-go/v2/tuple"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -156,7 +156,7 @@ func TestFromArrayMap(t *testing.T) {
 	src1 := A.From("a", "b", "c", "a")
 	frm := FromArrayMap[string, string](Mg.Second[string]())
 
-	f := frm(T.Replicate2[string])
+	f := frm(P.Of[string])
 
 	res1 := f(src1)
 
@@ -198,3 +198,555 @@ func TestHas(t *testing.T) {
 	assert.True(t, Has("a", nonEmpty))
 	assert.False(t, Has("c", nonEmpty))
 }
+
+func TestCollect(t *testing.T) {
+	data := map[string]int{
+		"a": 1,
+		"b": 2,
+		"c": 3,
+	}
+	collector := Collect[string, int, string](func(k string, v int) string {
+		return fmt.Sprintf("%s=%d", k, v)
+	})
+	result := collector(data)
+	sort.Strings(result)
+	assert.Equal(t, []string{"a=1", "b=2", "c=3"}, result)
+}
+
+func TestCollectOrd(t *testing.T) {
+	data := map[string]int{
+		"c": 3,
+		"a": 1,
+		"b": 2,
+	}
+	collector := CollectOrd[int, string](S.Ord)(func(k string, v int) string {
+		return fmt.Sprintf("%s=%d", k, v)
+	})
+	result := collector(data)
+	assert.Equal(t, []string{"a=1", "b=2", "c=3"}, result)
+}
+
+func TestReduce(t *testing.T) {
+	data := map[string]int{
+		"a": 1,
+		"b": 2,
+		"c": 3,
+	}
+	sum := Reduce[string, int, int](func(acc, v int) int {
+		return acc + v
+	}, 0)
+	result := sum(data)
+	assert.Equal(t, 6, result)
+}
+
+func TestReduceWithIndex(t *testing.T) {
+	data := map[string]int{
+		"a": 1,
+		"b": 2,
+		"c": 3,
+	}
+	concat := ReduceWithIndex[string, int, string](func(k string, acc string, v int) string {
+		if acc == "" {
+			return fmt.Sprintf("%s:%d", k, v)
+		}
+		return fmt.Sprintf("%s,%s:%d", acc, k, v)
+	}, "")
+	result := concat(data)
+	// Result order is non-deterministic, so check it contains all parts
+	assert.Contains(t, result, "a:1")
+	assert.Contains(t, result, "b:2")
+	assert.Contains(t, result, "c:3")
+}
+
+func TestMonadMap(t *testing.T) {
+	data := map[string]int{
+		"a": 1,
+		"b": 2,
+		"c": 3,
+	}
+	result := MonadMap(data, func(v int) int { return v * 2 })
+	assert.Equal(t, map[string]int{"a": 2, "b": 4, "c": 6}, result)
+}
+
+func TestMonadMapWithIndex(t *testing.T) {
+	data := map[string]int{
+		"a": 1,
+		"b": 2,
+	}
+	result := MonadMapWithIndex(data, func(k string, v int) string {
+		return fmt.Sprintf("%s=%d", k, v)
+	})
+	assert.Equal(t, map[string]string{"a": "a=1", "b": "b=2"}, result)
+}
+
+func TestMapWithIndex(t *testing.T) {
+	data := map[string]int{
+		"a": 1,
+		"b": 2,
+	}
+	mapper := MapWithIndex[string, int, string](func(k string, v int) string {
+		return fmt.Sprintf("%s=%d", k, v)
+	})
+	result := mapper(data)
+	assert.Equal(t, map[string]string{"a": "a=1", "b": "b=2"}, result)
+}
+
+func TestMonadLookup(t *testing.T) {
+	data := map[string]int{
+		"a": 1,
+		"b": 2,
+	}
+	assert.Equal(t, O.Some(1), MonadLookup(data, "a"))
+	assert.Equal(t, O.None[int](), MonadLookup(data, "c"))
+}
+
+func TestMerge(t *testing.T) {
+	left := map[string]int{"a": 1, "b": 2}
+	right := map[string]int{"b": 3, "c": 4}
+	result := Merge(right)(left)
+	assert.Equal(t, map[string]int{"a": 1, "b": 3, "c": 4}, result)
+}
+
+func TestSize(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2, "c": 3}
+	assert.Equal(t, 3, Size(data))
+	assert.Equal(t, 0, Size(Empty[string, int]()))
+}
+
+func TestToArray(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2}
+	result := ToArray(data)
+	assert.Len(t, result, 2)
+	// Check both entries exist (order is non-deterministic)
+	found := make(map[string]int)
+	for _, entry := range result {
+		found[P.Head(entry)] = P.Tail(entry)
+	}
+	assert.Equal(t, data, found)
+}
+
+func TestToEntries(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2}
+	result := ToEntries(data)
+	assert.Len(t, result, 2)
+}
+
+func TestFromEntries(t *testing.T) {
+	entries := Entries[string, int]{
+		P.MakePair("a", 1),
+		P.MakePair("b", 2),
+	}
+	result := FromEntries(entries)
+	assert.Equal(t, map[string]int{"a": 1, "b": 2}, result)
+}
+
+func TestUpsertAt(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2}
+	result := UpsertAt("c", 3)(data)
+	assert.Equal(t, map[string]int{"a": 1, "b": 2, "c": 3}, result)
+	// Original should be unchanged
+	assert.Equal(t, map[string]int{"a": 1, "b": 2}, data)
+
+	// Update existing
+	result2 := UpsertAt("a", 10)(data)
+	assert.Equal(t, map[string]int{"a": 10, "b": 2}, result2)
+}
+
+func TestDeleteAt(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2, "c": 3}
+	result := DeleteAt[string, int]("b")(data)
+	assert.Equal(t, map[string]int{"a": 1, "c": 3}, result)
+	// Original should be unchanged
+	assert.Equal(t, map[string]int{"a": 1, "b": 2, "c": 3}, data)
+}
+
+func TestSingleton(t *testing.T) {
+	result := Singleton("key", 42)
+	assert.Equal(t, map[string]int{"key": 42}, result)
+}
+
+func TestFilterMapWithIndex(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2, "c": 3}
+	filter := FilterMapWithIndex[string, int, int](func(k string, v int) O.Option[int] {
+		if v%2 == 0 {
+			return O.Some(v * 10)
+		}
+		return O.None[int]()
+	})
+	result := filter(data)
+	assert.Equal(t, map[string]int{"b": 20}, result)
+}
+
+func TestFilterMap(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2, "c": 3}
+	filter := FilterMap[string, int, int](func(v int) O.Option[int] {
+		if v%2 == 0 {
+			return O.Some(v * 10)
+		}
+		return O.None[int]()
+	})
+	result := filter(data)
+	assert.Equal(t, map[string]int{"b": 20}, result)
+}
+
+func TestFilter(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2, "c": 3}
+	filter := Filter[string, int](func(k string) bool {
+		return k != "b"
+	})
+	result := filter(data)
+	assert.Equal(t, map[string]int{"a": 1, "c": 3}, result)
+}
+
+func TestFilterWithIndex(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2, "c": 3}
+	filter := FilterWithIndex[string, int](func(k string, v int) bool {
+		return v%2 == 0
+	})
+	result := filter(data)
+	assert.Equal(t, map[string]int{"b": 2}, result)
+}
+
+func TestIsNil(t *testing.T) {
+	var nilMap map[string]int
+	nonNilMap := map[string]int{}
+
+	assert.True(t, IsNil(nilMap))
+	assert.False(t, IsNil(nonNilMap))
+}
+
+func TestIsNonNil(t *testing.T) {
+	var nilMap map[string]int
+	nonNilMap := map[string]int{}
+
+	assert.False(t, IsNonNil(nilMap))
+	assert.True(t, IsNonNil(nonNilMap))
+}
+
+func TestConstNil(t *testing.T) {
+	result := ConstNil[string, int]()
+	assert.Nil(t, result)
+	assert.True(t, IsNil(result))
+}
+
+func TestMonadChain(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2}
+	monoid := MergeMonoid[string, int]()
+	result := MonadChain(monoid, data, func(v int) map[string]int {
+		return map[string]int{
+			fmt.Sprintf("x%d", v): v * 10,
+		}
+	})
+	assert.Equal(t, map[string]int{"x1": 10, "x2": 20}, result)
+}
+
+func TestChain(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2}
+	monoid := MergeMonoid[string, int]()
+	chain := Chain[int, string, int](monoid)(func(v int) map[string]int {
+		return map[string]int{
+			fmt.Sprintf("x%d", v): v * 10,
+		}
+	})
+	result := chain(data)
+	assert.Equal(t, map[string]int{"x1": 10, "x2": 20}, result)
+}
+
+func TestFlatten(t *testing.T) {
+	nested := map[string]map[string]int{
+		"a": {"x": 1, "y": 2},
+		"b": {"z": 3},
+	}
+	monoid := MergeMonoid[string, int]()
+	flatten := Flatten(monoid)
+	result := flatten(nested)
+	assert.Equal(t, map[string]int{"x": 1, "y": 2, "z": 3}, result)
+}
+
+func TestFoldMap(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2, "c": 3}
+	// Use string monoid for simplicity
+	fold := FoldMap[string, int, string](S.Monoid)(func(v int) string {
+		return fmt.Sprintf("%d", v)
+	})
+	result := fold(data)
+	// Result contains all digits but order is non-deterministic
+	assert.Contains(t, result, "1")
+	assert.Contains(t, result, "2")
+	assert.Contains(t, result, "3")
+}
+
+func TestFold(t *testing.T) {
+	data := map[string]string{"a": "A", "b": "B", "c": "C"}
+	fold := Fold[string](S.Monoid)
+	result := fold(data)
+	// Result contains all letters but order is non-deterministic
+	assert.Contains(t, result, "A")
+	assert.Contains(t, result, "B")
+	assert.Contains(t, result, "C")
+}
+
+func TestKeysOrd(t *testing.T) {
+	data := map[string]int{"c": 3, "a": 1, "b": 2}
+	keys := KeysOrd[int](S.Ord)(data)
+	assert.Equal(t, []string{"a", "b", "c"}, keys)
+}
+
+func TestMonadFlap(t *testing.T) {
+	fns := map[string]func(int) int{
+		"double": func(x int) int { return x * 2 },
+		"triple": func(x int) int { return x * 3 },
+	}
+	result := MonadFlap(fns, 5)
+	assert.Equal(t, map[string]int{"double": 10, "triple": 15}, result)
+}
+
+func TestFlap(t *testing.T) {
+	fns := map[string]func(int) int{
+		"double": func(x int) int { return x * 2 },
+		"triple": func(x int) int { return x * 3 },
+	}
+	flap := Flap[int, string, int](5)
+	result := flap(fns)
+	assert.Equal(t, map[string]int{"double": 10, "triple": 15}, result)
+}
+
+func TestFromArray(t *testing.T) {
+	entries := Entries[string, int]{
+		P.MakePair("a", 1),
+		P.MakePair("b", 2),
+		P.MakePair("a", 3), // Duplicate key
+	}
+	// Use Second magma to keep last value
+	from := FromArray[string, int](Mg.Second[int]())
+	result := from(entries)
+	assert.Equal(t, map[string]int{"a": 3, "b": 2}, result)
+}
+
+func TestMonadAp(t *testing.T) {
+	fns := map[string]func(int) int{
+		"double": func(x int) int { return x * 2 },
+	}
+	vals := map[string]int{
+		"double": 5,
+	}
+	monoid := MergeMonoid[string, int]()
+	result := MonadAp(monoid, fns, vals)
+	assert.Equal(t, map[string]int{"double": 10}, result)
+}
+
+func TestAp(t *testing.T) {
+	fns := map[string]func(int) int{
+		"double": func(x int) int { return x * 2 },
+	}
+	vals := map[string]int{
+		"double": 5,
+	}
+	monoid := MergeMonoid[string, int]()
+	ap := Ap[int, string, int](monoid)(vals)
+	result := ap(fns)
+	assert.Equal(t, map[string]int{"double": 10}, result)
+}
+
+func TestOf(t *testing.T) {
+	result := Of("key", 42)
+	assert.Equal(t, map[string]int{"key": 42}, result)
+}
+
+func TestReduceRef(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2, "c": 3}
+	sum := ReduceRef[string, int, int](func(acc int, v *int) int {
+		return acc + *v
+	}, 0)
+	result := sum(data)
+	assert.Equal(t, 6, result)
+}
+
+func TestReduceRefWithIndex(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2}
+	concat := ReduceRefWithIndex[string, int, string](func(k string, acc string, v *int) string {
+		if acc == "" {
+			return fmt.Sprintf("%s:%d", k, *v)
+		}
+		return fmt.Sprintf("%s,%s:%d", acc, k, *v)
+	}, "")
+	result := concat(data)
+	assert.Contains(t, result, "a:1")
+	assert.Contains(t, result, "b:2")
+}
+
+func TestMonadMapRef(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2}
+	result := MonadMapRef(data, func(v *int) int { return *v * 2 })
+	assert.Equal(t, map[string]int{"a": 2, "b": 4}, result)
+}
+
+func TestMapRef(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2}
+	mapper := MapRef[string, int, int](func(v *int) int { return *v * 2 })
+	result := mapper(data)
+	assert.Equal(t, map[string]int{"a": 2, "b": 4}, result)
+}
+
+func TestMonadMapRefWithIndex(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2}
+	result := MonadMapRefWithIndex(data, func(k string, v *int) string {
+		return fmt.Sprintf("%s=%d", k, *v)
+	})
+	assert.Equal(t, map[string]string{"a": "a=1", "b": "b=2"}, result)
+}
+
+func TestMapRefWithIndex(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2}
+	mapper := MapRefWithIndex[string, int, string](func(k string, v *int) string {
+		return fmt.Sprintf("%s=%d", k, *v)
+	})
+	result := mapper(data)
+	assert.Equal(t, map[string]string{"a": "a=1", "b": "b=2"}, result)
+}
+
+func TestUnion(t *testing.T) {
+	left := map[string]int{"a": 1, "b": 2}
+	right := map[string]int{"b": 3, "c": 4}
+	// Union combines maps, with the magma resolving conflicts
+	// The order is union(left)(right), which means right is merged into left
+	// First magma keeps the first value (from right in this case)
+	union := Union[string, int](Mg.First[int]())
+	result := union(left)(right)
+	assert.Equal(t, map[string]int{"a": 1, "b": 3, "c": 4}, result)
+
+	// Second magma keeps the second value (from left in this case)
+	union2 := Union[string, int](Mg.Second[int]())
+	result2 := union2(left)(right)
+	assert.Equal(t, map[string]int{"a": 1, "b": 2, "c": 4}, result2)
+}
+
+func TestMonadChainWithIndex(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2}
+	monoid := MergeMonoid[string, string]()
+	result := MonadChainWithIndex(monoid, data, func(k string, v int) map[string]string {
+		return map[string]string{
+			fmt.Sprintf("%s%d", k, v): fmt.Sprintf("val%d", v),
+		}
+	})
+	assert.Equal(t, map[string]string{"a1": "val1", "b2": "val2"}, result)
+}
+
+func TestChainWithIndex(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2}
+	monoid := MergeMonoid[string, string]()
+	chain := ChainWithIndex[int, string, string](monoid)(func(k string, v int) map[string]string {
+		return map[string]string{
+			fmt.Sprintf("%s%d", k, v): fmt.Sprintf("val%d", v),
+		}
+	})
+	result := chain(data)
+	assert.Equal(t, map[string]string{"a1": "val1", "b2": "val2"}, result)
+}
+
+func TestFilterChainWithIndex(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 := MergeMonoid[string, string]()
+	res := FilterChainWithIndex[int](monoid)(f)(src)
+
+	assert.Equal(t, map[string]string{
+		"a": "a1",
+		"c": "c3",
+	}, res)
+}
+
+func TestFoldMapWithIndex(t *testing.T) {
+	data := map[string]int{"a": 1, "b": 2, "c": 3}
+	fold := FoldMapWithIndex[string, int, string](S.Monoid)(func(k string, v int) string {
+		return fmt.Sprintf("%s:%d", k, v)
+	})
+	result := fold(data)
+	// Result contains all pairs but order is non-deterministic
+	assert.Contains(t, result, "a:1")
+	assert.Contains(t, result, "b:2")
+	assert.Contains(t, result, "c:3")
+}
+
+func TestReduceOrd(t *testing.T) {
+	data := map[string]int{"c": 3, "a": 1, "b": 2}
+	sum := ReduceOrd[int, int](S.Ord)(func(acc, v int) int {
+		return acc + v
+	}, 0)
+	result := sum(data)
+	assert.Equal(t, 6, result)
+}
+
+func TestReduceOrdWithIndex(t *testing.T) {
+	data := map[string]int{"c": 3, "a": 1, "b": 2}
+	concat := ReduceOrdWithIndex[int, string](S.Ord)(func(k string, acc string, v int) string {
+		if acc == "" {
+			return fmt.Sprintf("%s:%d", k, v)
+		}
+		return fmt.Sprintf("%s,%s:%d", acc, k, v)
+	}, "")
+	result := concat(data)
+	// With Ord, keys should be in order
+	assert.Equal(t, "a:1,b:2,c:3", result)
+}
+
+func TestFoldMapOrdWithIndex(t *testing.T) {
+	data := map[string]int{"c": 3, "a": 1, "b": 2}
+	fold := FoldMapOrdWithIndex[string, int, string](S.Ord)(S.Monoid)(func(k string, v int) string {
+		return fmt.Sprintf("%s:%d,", k, v)
+	})
+	result := fold(data)
+	assert.Equal(t, "a:1,b:2,c:3,", result)
+}
+
+func TestFoldOrd(t *testing.T) {
+	data := map[string]string{"c": "C", "a": "A", "b": "B"}
+	fold := FoldOrd[string](S.Ord)(S.Monoid)
+	result := fold(data)
+	assert.Equal(t, "ABC", result)
+}
+
+func TestFromFoldableMap(t *testing.T) {
+	src := A.From("a", "b", "c", "a")
+	// Create a reducer function
+	reducer := A.Reduce[string, map[string]string]
+	from := FromFoldableMap[func(func(map[string]string, string) map[string]string, map[string]string) func([]string) map[string]string, string, []string, string, string](
+		Mg.Second[string](),
+		reducer,
+	)
+	f := from(P.Of[string])
+	result := f(src)
+	assert.Equal(t, map[string]string{
+		"a": "a",
+		"b": "b",
+		"c": "c",
+	}, result)
+}
+
+func TestFromFoldable(t *testing.T) {
+	entries := Entries[string, int]{
+		P.MakePair("a", 1),
+		P.MakePair("b", 2),
+		P.MakePair("a", 3), // Duplicate key
+	}
+	reducer := A.Reduce[Entry[string, int], map[string]int]
+	from := FromFoldable[[]Entry[string, int], func(func(map[string]int, Entry[string, int]) map[string]int, map[string]int) func([]Entry[string, int]) map[string]int, string, int](
+		Mg.Second[int](),
+		reducer,
+	)
+	result := from(entries)
+	assert.Equal(t, map[string]int{"a": 3, "b": 2}, result)
+}

v2/record/semigroup.go

@@ -20,14 +20,90 @@ import (
 	S "github.com/IBM/fp-go/v2/semigroup"
 )
 
+// UnionSemigroup creates a semigroup for maps that combines two maps using the provided
+// semigroup for resolving conflicts when the same key exists in both maps.
+//
+// When concatenating two maps:
+//   - Keys that exist in only one map are included in the result
+//   - Keys that exist in both maps have their values combined using the provided semigroup
+//
+// This is useful when you want custom conflict resolution logic beyond simple "first wins"
+// or "last wins" semantics.
+//
+// Example:
+//
+//	// Create a semigroup that sums values for duplicate keys
+//	sumSemigroup := number.SemigroupSum[int]()
+//	mapSemigroup := UnionSemigroup[string, int](sumSemigroup)
+//
+//	map1 := map[string]int{"a": 1, "b": 2}
+//	map2 := map[string]int{"b": 3, "c": 4}
+//	result := mapSemigroup.Concat(map1, map2)
+//	// result: {"a": 1, "b": 5, "c": 4}  // b values are summed: 2 + 3 = 5
+//
+// Example with string concatenation:
+//
+//	stringSemigroup := string.Semigroup
+//	mapSemigroup := UnionSemigroup[string, string](stringSemigroup)
+//
+//	map1 := map[string]string{"a": "Hello", "b": "World"}
+//	map2 := map[string]string{"b": "!", "c": "Goodbye"}
+//	result := mapSemigroup.Concat(map1, map2)
+//	// result: {"a": "Hello", "b": "World!", "c": "Goodbye"}
 func UnionSemigroup[K comparable, V any](s S.Semigroup[V]) S.Semigroup[map[K]V] {
 	return G.UnionSemigroup[map[K]V](s)
 }
 
+// UnionLastSemigroup creates a semigroup for maps where the last (right) value wins
+// when the same key exists in both maps being concatenated.
+//
+// This is the most common conflict resolution strategy and is equivalent to using
+// the standard map merge operation where right-side values take precedence.
+//
+// When concatenating two maps:
+//   - Keys that exist in only one map are included in the result
+//   - Keys that exist in both maps take the value from the second (right) map
+//
+// Example:
+//
+//	semigroup := UnionLastSemigroup[string, int]()
+//
+//	map1 := map[string]int{"a": 1, "b": 2}
+//	map2 := map[string]int{"b": 3, "c": 4}
+//	result := semigroup.Concat(map1, map2)
+//	// result: {"a": 1, "b": 3, "c": 4}  // b takes value from map2 (last wins)
+//
+// This is useful for:
+//   - Configuration overrides (later configs override earlier ones)
+//   - Applying updates to a base map
+//   - Merging user preferences where newer values should win
 func UnionLastSemigroup[K comparable, V any]() S.Semigroup[map[K]V] {
 	return G.UnionLastSemigroup[map[K]V]()
 }
 
+// UnionFirstSemigroup creates a semigroup for maps where the first (left) value wins
+// when the same key exists in both maps being concatenated.
+//
+// This is useful when you want to preserve original values and ignore updates for
+// keys that already exist.
+//
+// When concatenating two maps:
+//   - Keys that exist in only one map are included in the result
+//   - Keys that exist in both maps keep the value from the first (left) map
+//
+// Example:
+//
+//	semigroup := UnionFirstSemigroup[string, int]()
+//
+//	map1 := map[string]int{"a": 1, "b": 2}
+//	map2 := map[string]int{"b": 3, "c": 4}
+//	result := semigroup.Concat(map1, map2)
+//	// result: {"a": 1, "b": 2, "c": 4}  // b keeps value from map1 (first wins)
+//
+// This is useful for:
+//   - Default values (defaults are set first, user values don't override)
+//   - Caching (first cached value is kept, subsequent updates ignored)
+//   - Immutable registries (first registration wins, duplicates are ignored)
 func UnionFirstSemigroup[K comparable, V any]() S.Semigroup[map[K]V] {
 	return G.UnionFirstSemigroup[map[K]V]()
 }

v2/record/semigroup_test.go

@@ -0,0 +1,229 @@
+// Copyright (c) 2023 - 2025 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
+
+import (
+	"testing"
+
+	N "github.com/IBM/fp-go/v2/number"
+	S "github.com/IBM/fp-go/v2/string"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestUnionSemigroup(t *testing.T) {
+	// Test with sum semigroup - values should be added for duplicate keys
+	sumSemigroup := N.SemigroupSum[int]()
+	mapSemigroup := UnionSemigroup[string, int](sumSemigroup)
+
+	map1 := map[string]int{"a": 1, "b": 2}
+	map2 := map[string]int{"b": 3, "c": 4}
+	result := mapSemigroup.Concat(map1, map2)
+
+	expected := map[string]int{"a": 1, "b": 5, "c": 4}
+	assert.Equal(t, expected, result)
+}
+
+func TestUnionSemigroupString(t *testing.T) {
+	// Test with string semigroup - strings should be concatenated
+	stringSemigroup := S.Semigroup
+	mapSemigroup := UnionSemigroup[string, string](stringSemigroup)
+
+	map1 := map[string]string{"a": "Hello", "b": "World"}
+	map2 := map[string]string{"b": "!", "c": "Goodbye"}
+	result := mapSemigroup.Concat(map1, map2)
+
+	expected := map[string]string{"a": "Hello", "b": "World!", "c": "Goodbye"}
+	assert.Equal(t, expected, result)
+}
+
+func TestUnionSemigroupProduct(t *testing.T) {
+	// Test with product semigroup - values should be multiplied
+	prodSemigroup := N.SemigroupProduct[int]()
+	mapSemigroup := UnionSemigroup[string, int](prodSemigroup)
+
+	map1 := map[string]int{"a": 2, "b": 3}
+	map2 := map[string]int{"b": 4, "c": 5}
+	result := mapSemigroup.Concat(map1, map2)
+
+	expected := map[string]int{"a": 2, "b": 12, "c": 5}
+	assert.Equal(t, expected, result)
+}
+
+func TestUnionSemigroupEmpty(t *testing.T) {
+	// Test with empty maps
+	sumSemigroup := N.SemigroupSum[int]()
+	mapSemigroup := UnionSemigroup[string, int](sumSemigroup)
+
+	map1 := map[string]int{"a": 1}
+	empty := map[string]int{}
+
+	result1 := mapSemigroup.Concat(map1, empty)
+	assert.Equal(t, map1, result1)
+
+	result2 := mapSemigroup.Concat(empty, map1)
+	assert.Equal(t, map1, result2)
+}
+
+func TestUnionLastSemigroup(t *testing.T) {
+	// Test that last (right) value wins for duplicate keys
+	semigroup := UnionLastSemigroup[string, int]()
+
+	map1 := map[string]int{"a": 1, "b": 2}
+	map2 := map[string]int{"b": 3, "c": 4}
+	result := semigroup.Concat(map1, map2)
+
+	expected := map[string]int{"a": 1, "b": 3, "c": 4}
+	assert.Equal(t, expected, result)
+}
+
+func TestUnionLastSemigroupNoOverlap(t *testing.T) {
+	// Test with no overlapping keys
+	semigroup := UnionLastSemigroup[string, int]()
+
+	map1 := map[string]int{"a": 1, "b": 2}
+	map2 := map[string]int{"c": 3, "d": 4}
+	result := semigroup.Concat(map1, map2)
+
+	expected := map[string]int{"a": 1, "b": 2, "c": 3, "d": 4}
+	assert.Equal(t, expected, result)
+}
+
+func TestUnionLastSemigroupAllOverlap(t *testing.T) {
+	// Test with all keys overlapping
+	semigroup := UnionLastSemigroup[string, int]()
+
+	map1 := map[string]int{"a": 1, "b": 2}
+	map2 := map[string]int{"a": 10, "b": 20}
+	result := semigroup.Concat(map1, map2)
+
+	expected := map[string]int{"a": 10, "b": 20}
+	assert.Equal(t, expected, result)
+}
+
+func TestUnionLastSemigroupEmpty(t *testing.T) {
+	// Test with empty maps
+	semigroup := UnionLastSemigroup[string, int]()
+
+	map1 := map[string]int{"a": 1}
+	empty := map[string]int{}
+
+	result1 := semigroup.Concat(map1, empty)
+	assert.Equal(t, map1, result1)
+
+	result2 := semigroup.Concat(empty, map1)
+	assert.Equal(t, map1, result2)
+}
+
+func TestUnionFirstSemigroup(t *testing.T) {
+	// Test that first (left) value wins for duplicate keys
+	semigroup := UnionFirstSemigroup[string, int]()
+
+	map1 := map[string]int{"a": 1, "b": 2}
+	map2 := map[string]int{"b": 3, "c": 4}
+	result := semigroup.Concat(map1, map2)
+
+	expected := map[string]int{"a": 1, "b": 2, "c": 4}
+	assert.Equal(t, expected, result)
+}
+
+func TestUnionFirstSemigroupNoOverlap(t *testing.T) {
+	// Test with no overlapping keys
+	semigroup := UnionFirstSemigroup[string, int]()
+
+	map1 := map[string]int{"a": 1, "b": 2}
+	map2 := map[string]int{"c": 3, "d": 4}
+	result := semigroup.Concat(map1, map2)
+
+	expected := map[string]int{"a": 1, "b": 2, "c": 3, "d": 4}
+	assert.Equal(t, expected, result)
+}
+
+func TestUnionFirstSemigroupAllOverlap(t *testing.T) {
+	// Test with all keys overlapping
+	semigroup := UnionFirstSemigroup[string, int]()
+
+	map1 := map[string]int{"a": 1, "b": 2}
+	map2 := map[string]int{"a": 10, "b": 20}
+	result := semigroup.Concat(map1, map2)
+
+	expected := map[string]int{"a": 1, "b": 2}
+	assert.Equal(t, expected, result)
+}
+
+func TestUnionFirstSemigroupEmpty(t *testing.T) {
+	// Test with empty maps
+	semigroup := UnionFirstSemigroup[string, int]()
+
+	map1 := map[string]int{"a": 1}
+	empty := map[string]int{}
+
+	result1 := semigroup.Concat(map1, empty)
+	assert.Equal(t, map1, result1)
+
+	result2 := semigroup.Concat(empty, map1)
+	assert.Equal(t, map1, result2)
+}
+
+// Test associativity law for UnionSemigroup
+func TestUnionSemigroupAssociativity(t *testing.T) {
+	sumSemigroup := N.SemigroupSum[int]()
+	mapSemigroup := UnionSemigroup[string, int](sumSemigroup)
+
+	map1 := map[string]int{"a": 1}
+	map2 := map[string]int{"a": 2, "b": 3}
+	map3 := map[string]int{"b": 4, "c": 5}
+
+	// (map1 + map2) + map3
+	left := mapSemigroup.Concat(mapSemigroup.Concat(map1, map2), map3)
+	// map1 + (map2 + map3)
+	right := mapSemigroup.Concat(map1, mapSemigroup.Concat(map2, map3))
+
+	assert.Equal(t, left, right)
+}
+
+// Test associativity law for UnionLastSemigroup
+func TestUnionLastSemigroupAssociativity(t *testing.T) {
+	semigroup := UnionLastSemigroup[string, int]()
+
+	map1 := map[string]int{"a": 1}
+	map2 := map[string]int{"a": 2, "b": 3}
+	map3 := map[string]int{"b": 4, "c": 5}
+
+	// (map1 + map2) + map3
+	left := semigroup.Concat(semigroup.Concat(map1, map2), map3)
+	// map1 + (map2 + map3)
+	right := semigroup.Concat(map1, semigroup.Concat(map2, map3))
+
+	assert.Equal(t, left, right)
+}
+
+// Test associativity law for UnionFirstSemigroup
+func TestUnionFirstSemigroupAssociativity(t *testing.T) {
+	semigroup := UnionFirstSemigroup[string, int]()
+
+	map1 := map[string]int{"a": 1}
+	map2 := map[string]int{"a": 2, "b": 3}
+	map3 := map[string]int{"b": 4, "c": 5}
+
+	// (map1 + map2) + map3
+	left := semigroup.Concat(semigroup.Concat(map1, map2), map3)
+	// map1 + (map2 + map3)
+	right := semigroup.Concat(map1, semigroup.Concat(map2, map3))
+
+	assert.Equal(t, left, right)
+}
+
+// Made with Bob

v2/record/types.go

@@ -0,0 +1,154 @@
+// Copyright (c) 2023 - 2025 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
+
+import (
+	"github.com/IBM/fp-go/v2/pair"
+	"github.com/IBM/fp-go/v2/predicate"
+)
+
+type (
+
+	// Record represents a map with comparable keys and values of any type.
+	// This is the primary data structure for the record package, providing
+	// functional operations over Go's native map type.
+	//
+	// Example:
+	//
+	//	type UserRecord = Record[string, User]
+	//	users := UserRecord{
+	//	    "alice": User{Name: "Alice", Age: 30},
+	//	    "bob":   User{Name: "Bob", Age: 25},
+	//	}
+	Record[K comparable, V any] = map[K]V
+
+	// Predicate is a function that tests whether a key satisfies a condition.
+	// Used in filtering operations to determine which entries to keep.
+	//
+	// Example:
+	//
+	//	isVowel := func(k string) bool {
+	//	    return strings.ContainsAny(k, "aeiou")
+	//	}
+	Predicate[K any] = predicate.Predicate[K]
+
+	// PredicateWithIndex is a function that tests whether a key-value pair satisfies a condition.
+	// Used in filtering operations that need access to both key and value.
+	//
+	// Example:
+	//
+	//	isAdult := func(name string, user User) bool {
+	//	    return user.Age >= 18
+	//	}
+	PredicateWithIndex[K comparable, V any] = func(K, V) bool
+
+	// Operator transforms a record from one value type to another while preserving keys.
+	// This is the fundamental transformation type for record operations.
+	//
+	// Example:
+	//
+	//	doubleValues := Map(func(x int) int { return x * 2 })
+	//	result := doubleValues(Record[string, int]{"a": 1, "b": 2})
+	//	// result: {"a": 2, "b": 4}
+	Operator[K comparable, V1, V2 any] = func(Record[K, V1]) Record[K, V2]
+
+	// OperatorWithIndex transforms a record using both key and value information.
+	// Useful when the transformation depends on the key.
+	//
+	// Example:
+	//
+	//	prefixWithKey := MapWithIndex(func(k string, v string) string {
+	//	    return k + ":" + v
+	//	})
+	OperatorWithIndex[K comparable, V1, V2 any] = func(func(K, V1) V2) Operator[K, V1, V2]
+
+	// Kleisli represents a monadic function that transforms a value into a record.
+	// Used in chain operations for composing record-producing functions.
+	//
+	// Example:
+	//
+	//	expand := func(x int) Record[string, int] {
+	//	    return Record[string, int]{
+	//	        "double": x * 2,
+	//	        "triple": x * 3,
+	//	    }
+	//	}
+	Kleisli[K comparable, V1, V2 any] = func(V1) Record[K, V2]
+
+	// KleisliWithIndex is a monadic function that uses both key and value to produce a record.
+	//
+	// Example:
+	//
+	//	expandWithKey := func(k string, v int) Record[string, int] {
+	//	    return Record[string, int]{
+	//	        k + "_double": v * 2,
+	//	        k + "_triple": v * 3,
+	//	    }
+	//	}
+	KleisliWithIndex[K comparable, V1, V2 any] = func(K, V1) Record[K, V2]
+
+	// Reducer accumulates values from a record into a single result.
+	// The function receives the accumulator and current value, returning the new accumulator.
+	//
+	// Example:
+	//
+	//	sum := Reduce(func(acc int, v int) int {
+	//	    return acc + v
+	//	}, 0)
+	Reducer[K comparable, V, R any] = func(R, V) R
+
+	// ReducerWithIndex accumulates values using both key and value information.
+	//
+	// Example:
+	//
+	//	weightedSum := ReduceWithIndex(func(k string, acc int, v int) int {
+	//	    weight := len(k)
+	//	    return acc + (v * weight)
+	//	}, 0)
+	ReducerWithIndex[K comparable, V, R any] = func(K, R, V) R
+
+	// Collector transforms key-value pairs into a result type and collects them into an array.
+	//
+	// Example:
+	//
+	//	toStrings := Collect(func(k string, v int) string {
+	//	    return fmt.Sprintf("%s=%d", k, v)
+	//	})
+	Collector[K comparable, V, R any] = func(K, V) R
+
+	// Entry represents a single key-value pair from a record.
+	// This is an alias for Tuple2 to provide semantic clarity.
+	//
+	// Example:
+	//
+	//	entries := ToEntries(record)
+	//	for _, entry := range entries {
+	//	    key := entry.F1
+	//	    value := entry.F2
+	//	}
+	Entry[K comparable, V any] = pair.Pair[K, V]
+
+	// Entries is a slice of key-value pairs.
+	//
+	// Example:
+	//
+	//	entries := Entries[string, int]{
+	//	    T.MakeTuple2("a", 1),
+	//	    T.MakeTuple2("b", 2),
+	//	}
+	//	record := FromEntries(entries)
+	Entries[K comparable, V any] = []Entry[K, V]
+)