fix: improve lens handling

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

v2/cli/lens.go

@@ -116,18 +116,20 @@ func Make{{.Name}}Lenses() {{.Name}}Lenses {
 
 // Make{{.Name}}RefLenses creates a new {{.Name}}RefLenses with lenses for all fields
 func Make{{.Name}}RefLenses() {{.Name}}RefLenses {
-{{- range .Fields}}
-{{- if .IsOptional}}
-	iso{{.Name}} := I.FromZero[{{.TypeName}}]()
-{{- end}}
-{{- end}}
 	return {{.Name}}RefLenses{
 {{- range .Fields}}
 {{- if .IsOptional}}
-		{{.Name}}: L.MakeLensRef(
+{{- if .IsComparable}}
-			func(s *{{$.Name}}) O.Option[{{.TypeName}}] { return iso{{.Name}}.Get(s.{{.Name}}) },
+		{{.Name}}: LO.FromIso[*{{$.Name}}](I.FromZero[{{.TypeName}}]())(L.MakeLensStrict(
-			func(s *{{$.Name}}, v O.Option[{{.TypeName}}]) *{{$.Name}} { s.{{.Name}} = iso{{.Name}}.ReverseGet(v); return s },
+			func(s *{{$.Name}}) {{.TypeName}} { return s.{{.Name}} },
-		),
+			func(s *{{$.Name}}, v {{.TypeName}}) *{{$.Name}} { s.{{.Name}} = v; return s },
+		)),
+{{- else}}
+		{{.Name}}: LO.FromIso[*{{$.Name}}](I.FromZero[{{.TypeName}}]())(L.MakeLensRef(
+			func(s *{{$.Name}}) {{.TypeName}} { return s.{{.Name}} },
+			func(s *{{$.Name}}, v {{.TypeName}}) *{{$.Name}} { s.{{.Name}} = v; return s },
+		)),
+{{- end}}
 {{- else}}
 {{- if .IsComparable}}
 		{{.Name}}: L.MakeLensStrict(
@@ -460,9 +462,7 @@ func parseFile(filename string) ([]structInfo, string, error) {
 
 					// Check if the type is comparable (for non-optional fields)
 					// For optional fields, we don't need to check since they use LensO
-					if !isOptional {
+					isComparable = isComparableType(field.Type)
-						isComparable = isComparableType(field.Type)
-					}
 
 					// Extract imports from this field's type
 					fieldImports := make(map[string]string)

v2/cli/lens_test.go

@@ -472,7 +472,6 @@ type TypeTest struct {
 	assert.Equal(t, "Pointer", typeTest.Fields[2].Name)
 	assert.Equal(t, "*string", typeTest.Fields[2].TypeName)
 	assert.True(t, typeTest.Fields[2].IsOptional)
-	assert.False(t, typeTest.Fields[2].IsComparable, "IsComparable not set for optional fields")
 
 	// Slice - not comparable
 	assert.Equal(t, "Slice", typeTest.Fields[3].Name)
@@ -526,9 +525,6 @@ func TestLensRefTemplatesWithComparable(t *testing.T) {
 	assert.Contains(t, constructorStr, "Data: L.MakeLensRef(",
 		"non-comparable field Data should use MakeLensRef in RefLenses")
 
-	// Pointer field - optional, should use MakeLensRef
-	assert.Contains(t, constructorStr, "Pointer: L.MakeLensRef(",
-		"optional field Pointer should use MakeLensRef in RefLenses")
 }
 
 func TestGenerateLensHelpersWithComparable(t *testing.T) {

v2/optics/lens/iso/iso.go

@@ -24,18 +24,18 @@ import (
 )
 
 // FromNillable converts a nillable value to an option and back
-func FromNillable[T any]() I.Iso[*T, O.Option[T]] {
+func FromNillable[T any]() Iso[*T, Option[T]] {
 	return I.MakeIso(F.Flow2(
 		O.FromPredicate(F.IsNonNil[T]),
 		O.Map(F.Deref[T]),
 	),
-		O.Fold(F.Constant((*T)(nil)), F.Ref[T]),
+		O.Fold(F.ConstNil[T], F.Ref[T]),
 	)
 }
 
 // Compose converts a Lens to a property of `A` into a lens to a property of type `B`
 // the transformation is done via an ISO
-func Compose[S, A, B any](ab I.Iso[A, B]) func(sa L.Lens[S, A]) L.Lens[S, B] {
+func Compose[S, A, B any](ab Iso[A, B]) Operator[S, A, B] {
 	return F.Pipe2(
 		ab,
 		IL.IsoAsLens[A, B],

v2/optics/lens/iso/types.go

@@ -0,0 +1,14 @@
+package iso
+
+import (
+	"github.com/IBM/fp-go/v2/optics/iso"
+	"github.com/IBM/fp-go/v2/optics/lens"
+	"github.com/IBM/fp-go/v2/option"
+)
+
+type (
+	Option[A any]         = option.Option[A]
+	Iso[S, A any]         = iso.Iso[S, A]
+	Lens[S, A any]        = lens.Lens[S, A]
+	Operator[S, A, B any] = lens.Operator[S, A, B]
+)

v2/optics/lens/lens.go

@@ -435,7 +435,7 @@ func compose[GET ~func(S) B, SET ~func(S, B) S, S, A, B any](creator func(get GE
 //	person := Person{Name: "Alice", Address: Address{Street: "Main St"}}
 //	street := personStreetLens.Get(person)  // "Main St"
 //	updated := personStreetLens.Set("Oak Ave")(person)
-func Compose[S, A, B any](ab Lens[A, B]) func(Lens[S, A]) Lens[S, B] {
+func Compose[S, A, B any](ab Lens[A, B]) Operator[S, A, B] {
 	return compose(MakeLens[func(S) B, func(S, B) S], ab)
 }
 
@@ -477,7 +477,7 @@ func Compose[S, A, B any](ab Lens[A, B]) func(Lens[S, A]) Lens[S, B] {
 //	)
 //
 //	personStreetLens := F.Pipe1(addressLens, lens.ComposeRef[Person](streetLens))
-func ComposeRef[S, A, B any](ab Lens[A, B]) func(Lens[*S, A]) Lens[*S, B] {
+func ComposeRef[S, A, B any](ab Lens[A, B]) Operator[*S, A, B] {
 	return compose(MakeLensRef[func(*S) B, func(*S, B) *S], ab)
 }
 

v2/optics/lens/option/from.go

@@ -3,6 +3,7 @@ package option
 import (
 	F "github.com/IBM/fp-go/v2/function"
 	"github.com/IBM/fp-go/v2/optics/lens"
+	LI "github.com/IBM/fp-go/v2/optics/lens/iso"
 	O "github.com/IBM/fp-go/v2/option"
 )
 
@@ -95,3 +96,69 @@ func FromOption[S, A any](defaultValue A) func(sa LensO[S, A]) Lens[S, A] {
 func FromOptionRef[S, A any](defaultValue A) func(sa Lens[*S, Option[A]]) Lens[*S, A] {
 	return fromOption(lens.MakeLensRefCurried[S, A], defaultValue)
 }
+
+// FromIso converts a Lens[S, A] to a LensO[S, A] using an isomorphism.
+//
+// This function takes an isomorphism between A and Option[A] and uses it to
+// transform a regular lens into an optional lens. It's particularly useful when
+// you have a custom isomorphism that defines how to convert between a value
+// and its optional representation.
+//
+// The isomorphism must satisfy the round-trip laws:
+//  1. iso.ReverseGet(iso.Get(a)) == a for all a: A
+//  2. iso.Get(iso.ReverseGet(opt)) == opt for all opt: Option[A]
+//
+// Type Parameters:
+//   - S: The structure type containing the field
+//   - A: The type of the field being focused on
+//
+// Parameters:
+//   - iso: An isomorphism between A and Option[A] that defines the conversion
+//
+// Returns:
+//   - A function that takes a Lens[S, A] and returns a LensO[S, A]
+//
+// Example:
+//
+//	type Config struct {
+//	    timeout int
+//	}
+//
+//	// Create a lens to the timeout field
+//	timeoutLens := lens.MakeLens(
+//	    func(c Config) int { return c.timeout },
+//	    func(c Config, t int) Config { c.timeout = t; return c },
+//	)
+//
+//	// Create an isomorphism that treats 0 as None
+//	zeroAsNone := iso.MakeIso(
+//	    func(t int) option.Option[int] {
+//	        if t == 0 {
+//	            return option.None[int]()
+//	        }
+//	        return option.Some(t)
+//	    },
+//	    func(opt option.Option[int]) int {
+//	        return option.GetOrElse(func() int { return 0 })(opt)
+//	    },
+//	)
+//
+//	// Convert to optional lens
+//	optTimeoutLens := FromIso[Config, int](zeroAsNone)(timeoutLens)
+//
+//	config := Config{timeout: 0}
+//	opt := optTimeoutLens.Get(config)        // None[int]()
+//	updated := optTimeoutLens.Set(option.Some(30))(config) // Config{timeout: 30}
+//
+// Common Use Cases:
+//   - Converting between sentinel values (like 0, -1, "") and Option
+//   - Applying custom validation logic when converting to/from Option
+//   - Integrating with existing isomorphisms like FromNillable
+//
+// See also:
+//   - FromPredicate: For predicate-based optional conversion
+//   - FromNillable: For pointer-based optional conversion
+//   - FromOption: For converting from optional to non-optional with defaults
+func FromIso[S, A any](iso Iso[A, Option[A]]) func(Lens[S, A]) LensO[S, A] {
+	return LI.Compose[S](iso)
+}

v2/optics/lens/option/from_test.go

@@ -0,0 +1,481 @@
+// 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 option
+
+import (
+	"testing"
+
+	EQT "github.com/IBM/fp-go/v2/eq/testing"
+	F "github.com/IBM/fp-go/v2/function"
+	ISO "github.com/IBM/fp-go/v2/optics/iso"
+	L "github.com/IBM/fp-go/v2/optics/lens"
+	LT "github.com/IBM/fp-go/v2/optics/lens/testing"
+	O "github.com/IBM/fp-go/v2/option"
+	"github.com/stretchr/testify/assert"
+)
+
+// Test types
+type Config struct {
+	timeout int
+	retries int
+}
+
+type Settings struct {
+	maxConnections int
+	bufferSize     int
+}
+
+// TestFromIsoBasic tests basic functionality of FromIso
+func TestFromIsoBasic(t *testing.T) {
+	// Create an isomorphism that treats 0 as None
+	zeroAsNone := ISO.MakeIso(
+		func(t int) O.Option[int] {
+			if t == 0 {
+				return O.None[int]()
+			}
+			return O.Some(t)
+		},
+		func(opt O.Option[int]) int {
+			return O.GetOrElse(F.Constant(0))(opt)
+		},
+	)
+
+	// Create a lens to the timeout field
+	timeoutLens := L.MakeLens(
+		func(c Config) int { return c.timeout },
+		func(c Config, t int) Config { c.timeout = t; return c },
+	)
+
+	// Convert to optional lens using FromIso
+	optTimeoutLens := FromIso[Config, int](zeroAsNone)(timeoutLens)
+
+	t.Run("GetNone", func(t *testing.T) {
+		config := Config{timeout: 0, retries: 3}
+		result := optTimeoutLens.Get(config)
+		assert.True(t, O.IsNone(result))
+	})
+
+	t.Run("GetSome", func(t *testing.T) {
+		config := Config{timeout: 30, retries: 3}
+		result := optTimeoutLens.Get(config)
+		assert.True(t, O.IsSome(result))
+		assert.Equal(t, 30, O.GetOrElse(F.Constant(0))(result))
+	})
+
+	t.Run("SetNone", func(t *testing.T) {
+		config := Config{timeout: 30, retries: 3}
+		updated := optTimeoutLens.Set(O.None[int]())(config)
+		assert.Equal(t, 0, updated.timeout)
+		assert.Equal(t, 3, updated.retries) // Other fields unchanged
+	})
+
+	t.Run("SetSome", func(t *testing.T) {
+		config := Config{timeout: 0, retries: 3}
+		updated := optTimeoutLens.Set(O.Some(60))(config)
+		assert.Equal(t, 60, updated.timeout)
+		assert.Equal(t, 3, updated.retries) // Other fields unchanged
+	})
+
+	t.Run("SetPreservesOriginal", func(t *testing.T) {
+		original := Config{timeout: 30, retries: 3}
+		_ = optTimeoutLens.Set(O.Some(60))(original)
+		// Original should be unchanged
+		assert.Equal(t, 30, original.timeout)
+		assert.Equal(t, 3, original.retries)
+	})
+}
+
+// TestFromIsoWithNegativeSentinel tests using -1 as a sentinel value
+func TestFromIsoWithNegativeSentinel(t *testing.T) {
+	// Create an isomorphism that treats -1 as None
+	negativeOneAsNone := ISO.MakeIso(
+		func(n int) O.Option[int] {
+			if n == -1 {
+				return O.None[int]()
+			}
+			return O.Some(n)
+		},
+		func(opt O.Option[int]) int {
+			return O.GetOrElse(F.Constant(-1))(opt)
+		},
+	)
+
+	retriesLens := L.MakeLens(
+		func(c Config) int { return c.retries },
+		func(c Config, r int) Config { c.retries = r; return c },
+	)
+
+	optRetriesLens := FromIso[Config, int](negativeOneAsNone)(retriesLens)
+
+	t.Run("GetNoneForNegativeOne", func(t *testing.T) {
+		config := Config{timeout: 30, retries: -1}
+		result := optRetriesLens.Get(config)
+		assert.True(t, O.IsNone(result))
+	})
+
+	t.Run("GetSomeForZero", func(t *testing.T) {
+		config := Config{timeout: 30, retries: 0}
+		result := optRetriesLens.Get(config)
+		assert.True(t, O.IsSome(result))
+		assert.Equal(t, 0, O.GetOrElse(F.Constant(-1))(result))
+	})
+
+	t.Run("SetNoneToNegativeOne", func(t *testing.T) {
+		config := Config{timeout: 30, retries: 5}
+		updated := optRetriesLens.Set(O.None[int]())(config)
+		assert.Equal(t, -1, updated.retries)
+	})
+}
+
+// TestFromIsoLaws verifies that FromIso satisfies lens laws
+func TestFromIsoLaws(t *testing.T) {
+	// Create an isomorphism
+	zeroAsNone := ISO.MakeIso(
+		func(t int) O.Option[int] {
+			if t == 0 {
+				return O.None[int]()
+			}
+			return O.Some(t)
+		},
+		func(opt O.Option[int]) int {
+			return O.GetOrElse(F.Constant(0))(opt)
+		},
+	)
+
+	timeoutLens := L.MakeLens(
+		func(c Config) int { return c.timeout },
+		func(c Config, t int) Config { c.timeout = t; return c },
+	)
+
+	optTimeoutLens := FromIso[Config, int](zeroAsNone)(timeoutLens)
+
+	eqOptInt := O.Eq(EQT.Eq[int]())
+	eqConfig := EQT.Eq[Config]()
+
+	config := Config{timeout: 30, retries: 3}
+	newValue := O.Some(60)
+
+	// Law 1: GetSet - lens.Set(lens.Get(s))(s) == s
+	t.Run("GetSetLaw", func(t *testing.T) {
+		result := optTimeoutLens.Set(optTimeoutLens.Get(config))(config)
+		assert.True(t, eqConfig.Equals(config, result))
+	})
+
+	// Law 2: SetGet - lens.Get(lens.Set(a)(s)) == a
+	t.Run("SetGetLaw", func(t *testing.T) {
+		result := optTimeoutLens.Get(optTimeoutLens.Set(newValue)(config))
+		assert.True(t, eqOptInt.Equals(newValue, result))
+	})
+
+	// Law 3: SetSet - lens.Set(a2)(lens.Set(a1)(s)) == lens.Set(a2)(s)
+	t.Run("SetSetLaw", func(t *testing.T) {
+		a1 := O.Some(60)
+		a2 := O.None[int]()
+		result1 := optTimeoutLens.Set(a2)(optTimeoutLens.Set(a1)(config))
+		result2 := optTimeoutLens.Set(a2)(config)
+		assert.True(t, eqConfig.Equals(result1, result2))
+	})
+
+	// Use the testing helper to verify all laws
+	t.Run("AllLaws", func(t *testing.T) {
+		laws := LT.AssertLaws(t, eqOptInt, eqConfig)(optTimeoutLens)
+		assert.True(t, laws(config, O.Some(100)))
+		assert.True(t, laws(Config{timeout: 0, retries: 5}, O.None[int]()))
+	})
+}
+
+// TestFromIsoComposition tests composing FromIso with other lenses
+func TestFromIsoComposition(t *testing.T) {
+	type Application struct {
+		config Config
+	}
+
+	// Isomorphism for zero as none
+	zeroAsNone := ISO.MakeIso(
+		func(t int) O.Option[int] {
+			if t == 0 {
+				return O.None[int]()
+			}
+			return O.Some(t)
+		},
+		func(opt O.Option[int]) int {
+			return O.GetOrElse(F.Constant(0))(opt)
+		},
+	)
+
+	// Lens to config field
+	configLens := L.MakeLens(
+		func(a Application) Config { return a.config },
+		func(a Application, c Config) Application { a.config = c; return a },
+	)
+
+	// Lens to timeout field
+	timeoutLens := L.MakeLens(
+		func(c Config) int { return c.timeout },
+		func(c Config, t int) Config { c.timeout = t; return c },
+	)
+
+	// Compose: Application -> Config -> timeout (as Option)
+	optTimeoutFromConfig := FromIso[Config, int](zeroAsNone)(timeoutLens)
+	optTimeoutFromApp := F.Pipe1(
+		configLens,
+		L.Compose[Application](optTimeoutFromConfig),
+	)
+
+	app := Application{config: Config{timeout: 0, retries: 3}}
+
+	t.Run("ComposedGet", func(t *testing.T) {
+		result := optTimeoutFromApp.Get(app)
+		assert.True(t, O.IsNone(result))
+	})
+
+	t.Run("ComposedSet", func(t *testing.T) {
+		updated := optTimeoutFromApp.Set(O.Some(45))(app)
+		assert.Equal(t, 45, updated.config.timeout)
+		assert.Equal(t, 3, updated.config.retries)
+	})
+}
+
+// TestFromIsoModify tests using Modify with FromIso-based lenses
+func TestFromIsoModify(t *testing.T) {
+	zeroAsNone := ISO.MakeIso(
+		func(t int) O.Option[int] {
+			if t == 0 {
+				return O.None[int]()
+			}
+			return O.Some(t)
+		},
+		func(opt O.Option[int]) int {
+			return O.GetOrElse(F.Constant(0))(opt)
+		},
+	)
+
+	timeoutLens := L.MakeLens(
+		func(c Config) int { return c.timeout },
+		func(c Config, t int) Config { c.timeout = t; return c },
+	)
+
+	optTimeoutLens := FromIso[Config, int](zeroAsNone)(timeoutLens)
+
+	t.Run("ModifyNoneToSome", func(t *testing.T) {
+		config := Config{timeout: 0, retries: 3}
+		// Map None to Some(10)
+		modified := L.Modify[Config](O.Map(func(x int) int { return x + 10 }))(optTimeoutLens)(config)
+		// Since it was None, Map doesn't apply, stays None (0)
+		assert.Equal(t, 0, modified.timeout)
+	})
+
+	t.Run("ModifySomeValue", func(t *testing.T) {
+		config := Config{timeout: 30, retries: 3}
+		// Double the timeout value
+		modified := L.Modify[Config](O.Map(func(x int) int { return x * 2 }))(optTimeoutLens)(config)
+		assert.Equal(t, 60, modified.timeout)
+	})
+
+	t.Run("ModifyWithAlt", func(t *testing.T) {
+		config := Config{timeout: 0, retries: 3}
+		// Use Alt to provide a default
+		modified := L.Modify[Config](func(opt O.Option[int]) O.Option[int] {
+			return O.Alt(F.Constant(O.Some(10)))(opt)
+		})(optTimeoutLens)(config)
+		assert.Equal(t, 10, modified.timeout)
+	})
+}
+
+// TestFromIsoWithStringEmpty tests using empty string as None
+func TestFromIsoWithStringEmpty(t *testing.T) {
+	type User struct {
+		name  string
+		email string
+	}
+
+	// Isomorphism that treats empty string as None
+	emptyAsNone := ISO.MakeIso(
+		func(s string) O.Option[string] {
+			if s == "" {
+				return O.None[string]()
+			}
+			return O.Some(s)
+		},
+		func(opt O.Option[string]) string {
+			return O.GetOrElse(F.Constant(""))(opt)
+		},
+	)
+
+	emailLens := L.MakeLens(
+		func(u User) string { return u.email },
+		func(u User, e string) User { u.email = e; return u },
+	)
+
+	optEmailLens := FromIso[User, string](emptyAsNone)(emailLens)
+
+	t.Run("EmptyStringAsNone", func(t *testing.T) {
+		user := User{name: "Alice", email: ""}
+		result := optEmailLens.Get(user)
+		assert.True(t, O.IsNone(result))
+	})
+
+	t.Run("NonEmptyStringAsSome", func(t *testing.T) {
+		user := User{name: "Alice", email: "alice@example.com"}
+		result := optEmailLens.Get(user)
+		assert.True(t, O.IsSome(result))
+		assert.Equal(t, "alice@example.com", O.GetOrElse(F.Constant(""))(result))
+	})
+
+	t.Run("SetNoneToEmpty", func(t *testing.T) {
+		user := User{name: "Alice", email: "alice@example.com"}
+		updated := optEmailLens.Set(O.None[string]())(user)
+		assert.Equal(t, "", updated.email)
+	})
+}
+
+// TestFromIsoRoundTrip tests round-trip conversions
+func TestFromIsoRoundTrip(t *testing.T) {
+	zeroAsNone := ISO.MakeIso(
+		func(t int) O.Option[int] {
+			if t == 0 {
+				return O.None[int]()
+			}
+			return O.Some(t)
+		},
+		func(opt O.Option[int]) int {
+			return O.GetOrElse(F.Constant(0))(opt)
+		},
+	)
+
+	maxConnectionsLens := L.MakeLens(
+		func(s Settings) int { return s.maxConnections },
+		func(s Settings, m int) Settings { s.maxConnections = m; return s },
+	)
+
+	optMaxConnectionsLens := FromIso[Settings, int](zeroAsNone)(maxConnectionsLens)
+
+	t.Run("RoundTripThroughGet", func(t *testing.T) {
+		settings := Settings{maxConnections: 100, bufferSize: 1024}
+		// Get the value, then Set it back
+		opt := optMaxConnectionsLens.Get(settings)
+		restored := optMaxConnectionsLens.Set(opt)(settings)
+		assert.Equal(t, settings, restored)
+	})
+
+	t.Run("RoundTripThroughSet", func(t *testing.T) {
+		settings := Settings{maxConnections: 0, bufferSize: 1024}
+		// Set a new value, then Get it
+		newOpt := O.Some(200)
+		updated := optMaxConnectionsLens.Set(newOpt)(settings)
+		retrieved := optMaxConnectionsLens.Get(updated)
+		assert.True(t, O.Eq(EQT.Eq[int]()).Equals(newOpt, retrieved))
+	})
+
+	t.Run("RoundTripWithNone", func(t *testing.T) {
+		settings := Settings{maxConnections: 100, bufferSize: 1024}
+		// Set None, then get it back
+		updated := optMaxConnectionsLens.Set(O.None[int]())(settings)
+		retrieved := optMaxConnectionsLens.Get(updated)
+		assert.True(t, O.IsNone(retrieved))
+	})
+}
+
+// TestFromIsoChaining tests chaining multiple FromIso transformations
+func TestFromIsoChaining(t *testing.T) {
+	// Create two different isomorphisms
+	zeroAsNone := ISO.MakeIso(
+		func(t int) O.Option[int] {
+			if t == 0 {
+				return O.None[int]()
+			}
+			return O.Some(t)
+		},
+		func(opt O.Option[int]) int {
+			return O.GetOrElse(F.Constant(0))(opt)
+		},
+	)
+
+	timeoutLens := L.MakeLens(
+		func(c Config) int { return c.timeout },
+		func(c Config, t int) Config { c.timeout = t; return c },
+	)
+
+	optTimeoutLens := FromIso[Config, int](zeroAsNone)(timeoutLens)
+
+	config := Config{timeout: 30, retries: 3}
+
+	t.Run("ChainedOperations", func(t *testing.T) {
+		// Chain multiple operations
+		result := F.Pipe2(
+			config,
+			optTimeoutLens.Set(O.Some(60)),
+			optTimeoutLens.Set(O.None[int]()),
+		)
+		assert.Equal(t, 0, result.timeout)
+	})
+}
+
+// TestFromIsoMultipleFields tests using FromIso on multiple fields
+func TestFromIsoMultipleFields(t *testing.T) {
+	zeroAsNone := ISO.MakeIso(
+		func(t int) O.Option[int] {
+			if t == 0 {
+				return O.None[int]()
+			}
+			return O.Some(t)
+		},
+		func(opt O.Option[int]) int {
+			return O.GetOrElse(F.Constant(0))(opt)
+		},
+	)
+
+	timeoutLens := L.MakeLens(
+		func(c Config) int { return c.timeout },
+		func(c Config, t int) Config { c.timeout = t; return c },
+	)
+
+	retriesLens := L.MakeLens(
+		func(c Config) int { return c.retries },
+		func(c Config, r int) Config { c.retries = r; return c },
+	)
+
+	optTimeoutLens := FromIso[Config, int](zeroAsNone)(timeoutLens)
+	optRetriesLens := FromIso[Config, int](zeroAsNone)(retriesLens)
+
+	t.Run("IndependentFields", func(t *testing.T) {
+		config := Config{timeout: 0, retries: 5}
+
+		// Get both fields
+		timeoutOpt := optTimeoutLens.Get(config)
+		retriesOpt := optRetriesLens.Get(config)
+
+		assert.True(t, O.IsNone(timeoutOpt))
+		assert.True(t, O.IsSome(retriesOpt))
+		assert.Equal(t, 5, O.GetOrElse(F.Constant(0))(retriesOpt))
+	})
+
+	t.Run("SetBothFields", func(t *testing.T) {
+		config := Config{timeout: 0, retries: 0}
+
+		// Set both fields
+		updated := F.Pipe2(
+			config,
+			optTimeoutLens.Set(O.Some(30)),
+			optRetriesLens.Set(O.Some(3)),
+		)
+
+		assert.Equal(t, 30, updated.timeout)
+		assert.Equal(t, 3, updated.retries)
+	})
+}
+
+// Made with Bob

v2/optics/lens/option/types.go

@@ -17,6 +17,7 @@ package option
 
 import (
 	"github.com/IBM/fp-go/v2/endomorphism"
+	"github.com/IBM/fp-go/v2/optics/iso"
 	"github.com/IBM/fp-go/v2/optics/lens"
 	"github.com/IBM/fp-go/v2/option"
 )
@@ -91,4 +92,6 @@ type (
 	//   optLens := lens.FromNillableRef(timeoutLens)
 	//   // optLens is a LensO[*Config, *int]
 	LensO[S, A any] = Lens[S, Option[A]]
+
+	Iso[S, A any] = iso.Iso[S, A]
 )

v2/optics/lens/types.go

@@ -80,4 +80,7 @@ type (
 		// with the focused value updated to a. The original structure is never modified.
 		Set func(a A) Endomorphism[S]
 	}
+
+	Kleisli[S, A, B any]  = func(A) Lens[S, B]
+	Operator[S, A, B any] = Kleisli[S, Lens[S, A], B]
 )

v2/samples/lens/example_test.go

@@ -20,6 +20,7 @@ import (
 
 	F "github.com/IBM/fp-go/v2/function"
 	L "github.com/IBM/fp-go/v2/optics/lens"
+	O "github.com/IBM/fp-go/v2/option"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -196,3 +197,147 @@ func TestPersonRefLensesIdempotent(t *testing.T) {
 	assert.Equal(t, "bob@example.com", differentEmail.Email)
 	assert.Equal(t, "alice@example.com", person.Email, "Original should be unchanged")
 }
+
+func TestPersonRefLensesOptionalIdempotent(t *testing.T) {
+	// Test that setting an optional field to the same value returns the identical pointer
+	// This is important for performance and correctness in functional programming
+
+	// Test with Phone field set to a value
+	phoneValue := "555-1234"
+	person := &Person{
+		Name:  "Alice",
+		Age:   30,
+		Email: "alice@example.com",
+		Phone: &phoneValue,
+	}
+
+	refLenses := MakePersonRefLenses()
+
+	// Test that setting Phone to the same value returns the same pointer
+	samePhone := refLenses.Phone.Set(O.Some(&phoneValue))(person)
+	assert.Same(t, person, samePhone, "Setting Phone to same value should return identical pointer")
+
+	// Test with Phone field set to nil
+	personNoPhone := &Person{
+		Name:  "Bob",
+		Age:   25,
+		Email: "bob@example.com",
+		Phone: nil,
+	}
+
+	// Setting Phone to None when it's already nil should return same pointer
+	sameNilPhone := refLenses.Phone.Set(O.None[*string]())(personNoPhone)
+	assert.Same(t, personNoPhone, sameNilPhone, "Setting Phone to None when already nil should return identical pointer")
+
+	// Test that setting to a different value creates a new pointer
+	newPhoneValue := "555-5678"
+	differentPhone := refLenses.Phone.Set(O.Some(&newPhoneValue))(person)
+	assert.NotSame(t, person, differentPhone, "Setting Phone to different value should return new pointer")
+	assert.Equal(t, &newPhoneValue, differentPhone.Phone)
+	assert.Equal(t, &phoneValue, person.Phone, "Original should be unchanged")
+
+	// Test setting from nil to Some creates new pointer
+	somePhone := refLenses.Phone.Set(O.Some(&phoneValue))(personNoPhone)
+	assert.NotSame(t, personNoPhone, somePhone, "Setting Phone from nil to Some should return new pointer")
+	assert.Equal(t, &phoneValue, somePhone.Phone)
+	assert.Nil(t, personNoPhone.Phone, "Original should be unchanged")
+
+	// Test setting from Some to None creates new pointer
+	nonePhone := refLenses.Phone.Set(O.None[*string]())(person)
+	assert.NotSame(t, person, nonePhone, "Setting Phone from Some to None should return new pointer")
+	assert.Nil(t, nonePhone.Phone)
+	assert.Equal(t, &phoneValue, person.Phone, "Original should be unchanged")
+}
+
+func TestAddressRefLensesOptionalIdempotent(t *testing.T) {
+	// Test Address.State optional field idempotency
+
+	stateValue := "California"
+	address := &Address{
+		Street:  "123 Main St",
+		City:    "Los Angeles",
+		ZipCode: "90001",
+		Country: "USA",
+		State:   &stateValue,
+	}
+
+	refLenses := MakeAddressRefLenses()
+
+	// Test that setting State to the same value returns the same pointer
+	sameState := refLenses.State.Set(O.Some(&stateValue))(address)
+	assert.Same(t, address, sameState, "Setting State to same value should return identical pointer")
+
+	// Test with State field set to nil
+	addressNoState := &Address{
+		Street:  "456 Oak Ave",
+		City:    "Boston",
+		ZipCode: "02101",
+		Country: "USA",
+		State:   nil,
+	}
+
+	// Setting State to None when it's already nil should return same pointer
+	sameNilState := refLenses.State.Set(O.None[*string]())(addressNoState)
+	assert.Same(t, addressNoState, sameNilState, "Setting State to None when already nil should return identical pointer")
+
+	// Test that setting to a different value creates a new pointer
+	newStateValue := "New York"
+	differentState := refLenses.State.Set(O.Some(&newStateValue))(address)
+	assert.NotSame(t, address, differentState, "Setting State to different value should return new pointer")
+	assert.Equal(t, &newStateValue, differentState.State)
+	assert.Equal(t, &stateValue, address.State, "Original should be unchanged")
+}
+
+func TestCompanyRefLensesOptionalIdempotent(t *testing.T) {
+	// Test Company.Website optional field idempotency
+
+	websiteValue := "https://example.com"
+	company := &Company{
+		Name: "Tech Inc",
+		Address: Address{
+			Street:  "789 Tech Blvd",
+			City:    "San Francisco",
+			ZipCode: "94102",
+			Country: "USA",
+		},
+		CEO: Person{
+			Name:  "Jane Doe",
+			Age:   45,
+			Email: "jane@techinc.com",
+		},
+		Website: &websiteValue,
+	}
+
+	refLenses := MakeCompanyRefLenses()
+
+	// Test that setting Website to the same value returns the same pointer
+	sameWebsite := refLenses.Website.Set(O.Some(&websiteValue))(company)
+	assert.Same(t, company, sameWebsite, "Setting Website to same value should return identical pointer")
+
+	// Test with Website field set to nil
+	companyNoWebsite := &Company{
+		Name: "Startup LLC",
+		Address: Address{
+			Street:  "101 Innovation Way",
+			City:    "Austin",
+			ZipCode: "78701",
+			Country: "USA",
+		},
+		CEO: Person{
+			Name:  "John Smith",
+			Age:   35,
+			Email: "john@startup.com",
+		},
+	}
+
+	// Setting Website to None when it's already nil should return same pointer
+	sameNilWebsite := refLenses.Website.Set(O.None[*string]())(companyNoWebsite)
+	assert.Same(t, companyNoWebsite, sameNilWebsite, "Setting Website to None when already nil should return identical pointer")
+
+	// Test that setting to a different value creates a new pointer
+	newWebsiteValue := "https://newsite.com"
+	differentWebsite := refLenses.Website.Set(O.Some(&newWebsiteValue))(company)
+	assert.NotSame(t, company, differentWebsite, "Setting Website to different value should return new pointer")
+	assert.Equal(t, &newWebsiteValue, differentWebsite.Website)
+	assert.Equal(t, &websiteValue, company.Website, "Original should be unchanged")
+}

v2/samples/lens/gen_lens.go

@@ -2,7 +2,7 @@ package lens
 
 // Code generated by go generate; DO NOT EDIT.
 // This file was generated by robots at
-// 2025-11-12 17:16:40.1431921 +0100 CET m=+0.003694701
+// 2025-11-12 18:15:07.69943 +0100 CET m=+0.005345401
 
 import (
 	L "github.com/IBM/fp-go/v2/optics/lens"
@@ -53,7 +53,6 @@ func MakePersonLenses() PersonLenses {
 
 // MakePersonRefLenses creates a new PersonRefLenses with lenses for all fields
 func MakePersonRefLenses() PersonRefLenses {
-	isoPhone := I.FromZero[*string]()
 	return PersonRefLenses{
 		Name: L.MakeLensStrict(
 			func(s *Person) string { return s.Name },
@@ -67,10 +66,10 @@ func MakePersonRefLenses() PersonRefLenses {
 			func(s *Person) string { return s.Email },
 			func(s *Person, v string) *Person { s.Email = v; return s },
 		),
-		Phone: L.MakeLensRef(
+		Phone: LO.FromIso[*Person](I.FromZero[*string]())(L.MakeLensStrict(
-			func(s *Person) O.Option[*string] { return isoPhone.Get(s.Phone) },
+			func(s *Person) *string { return s.Phone },
-			func(s *Person, v O.Option[*string]) *Person { s.Phone = isoPhone.ReverseGet(v); return s },
+			func(s *Person, v *string) *Person { s.Phone = v; return s },
-		),
+		)),
 	}
 }
 
@@ -121,7 +120,6 @@ func MakeAddressLenses() AddressLenses {
 
 // MakeAddressRefLenses creates a new AddressRefLenses with lenses for all fields
 func MakeAddressRefLenses() AddressRefLenses {
-	isoState := I.FromZero[*string]()
 	return AddressRefLenses{
 		Street: L.MakeLensStrict(
 			func(s *Address) string { return s.Street },
@@ -139,10 +137,10 @@ func MakeAddressRefLenses() AddressRefLenses {
 			func(s *Address) string { return s.Country },
 			func(s *Address, v string) *Address { s.Country = v; return s },
 		),
-		State: L.MakeLensRef(
+		State: LO.FromIso[*Address](I.FromZero[*string]())(L.MakeLensStrict(
-			func(s *Address) O.Option[*string] { return isoState.Get(s.State) },
+			func(s *Address) *string { return s.State },
-			func(s *Address, v O.Option[*string]) *Address { s.State = isoState.ReverseGet(v); return s },
+			func(s *Address, v *string) *Address { s.State = v; return s },
-		),
+		)),
 	}
 }
 
@@ -187,7 +185,6 @@ func MakeCompanyLenses() CompanyLenses {
 
 // MakeCompanyRefLenses creates a new CompanyRefLenses with lenses for all fields
 func MakeCompanyRefLenses() CompanyRefLenses {
-	isoWebsite := I.FromZero[*string]()
 	return CompanyRefLenses{
 		Name: L.MakeLensStrict(
 			func(s *Company) string { return s.Name },
@@ -201,10 +198,10 @@ func MakeCompanyRefLenses() CompanyRefLenses {
 			func(s *Company) Person { return s.CEO },
 			func(s *Company, v Person) *Company { s.CEO = v; return s },
 		),
-		Website: L.MakeLensRef(
+		Website: LO.FromIso[*Company](I.FromZero[*string]())(L.MakeLensStrict(
-			func(s *Company) O.Option[*string] { return isoWebsite.Get(s.Website) },
+			func(s *Company) *string { return s.Website },
-			func(s *Company, v O.Option[*string]) *Company { s.Website = isoWebsite.ReverseGet(v); return s },
+			func(s *Company, v *string) *Company { s.Website = v; return s },
-		),
+		)),
 	}
 }
 
@@ -237,15 +234,14 @@ func MakeCheckOptionLenses() CheckOptionLenses {
 
 // MakeCheckOptionRefLenses creates a new CheckOptionRefLenses with lenses for all fields
 func MakeCheckOptionRefLenses() CheckOptionRefLenses {
-	isoValue := I.FromZero[string]()
 	return CheckOptionRefLenses{
 		Name: L.MakeLensRef(
 			func(s *CheckOption) option.Option[string] { return s.Name },
 			func(s *CheckOption, v option.Option[string]) *CheckOption { s.Name = v; return s },
 		),
-		Value: L.MakeLensRef(
+		Value: LO.FromIso[*CheckOption](I.FromZero[string]())(L.MakeLensStrict(
-			func(s *CheckOption) O.Option[string] { return isoValue.Get(s.Value) },
+			func(s *CheckOption) string { return s.Value },
-			func(s *CheckOption, v O.Option[string]) *CheckOption { s.Value = isoValue.ReverseGet(v); return s },
+			func(s *CheckOption, v string) *CheckOption { s.Value = v; return s },
-		),
+		)),
 	}
 }