fix: refactor either type (#102)

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

context/readerioeither/file/file_test.go

@@ -47,5 +47,5 @@ func ExampleReadFile() {
 	fmt.Println(result())
 
 	// Output:
-	// Right[<nil>, string](Carsten)
+	// Right[string](Carsten)
 }

context/readerioeither/generic/reader.go

@@ -182,10 +182,7 @@ func withCancelCauseFunc[
 		ma,
 		IOE.Swap[GIOA, func() E.Either[A, error]],
 		IOE.ChainFirstIOK[func() E.Either[A, error], func() any](func(err error) func() any {
-			return IO.MakeIO[func() any](func() any {
+			return IO.FromImpure[func() any](func() { cancel(err) })
-				cancel(err)
-				return nil
-			})
 		}),
 		IOE.Swap[func() E.Either[A, error], GIOA],
 	)

either/core.go

@@ -23,17 +23,16 @@ type (
 	// Either defines a data structure that logically holds either an E or an A. The flag discriminates the cases
 	Either[E, A any] struct {
 		isLeft bool
-		left   E
+		value  any
-		right  A
 	}
 )
 
 // String prints some debug info for the object
 func (s Either[E, A]) String() string {
 	if s.isLeft {
-		return fmt.Sprintf("Left[%T, %T](%v)", s.left, s.right, s.left)
+		return fmt.Sprintf("Left[%T](%v)", s.value, s.value)
 	}
-	return fmt.Sprintf("Right[%T, %T](%v)", s.left, s.right, s.right)
+	return fmt.Sprintf("Right[%T](%v)", s.value, s.value)
 }
 
 // Format prints some debug info for the object
@@ -58,23 +57,29 @@ func IsRight[E, A any](val Either[E, A]) bool {
 
 // Left creates a new instance of an [Either] representing the left value.
 func Left[A, E any](value E) Either[E, A] {
-	return Either[E, A]{isLeft: true, left: value}
+	return Either[E, A]{true, value}
 }
 
 // Right creates a new instance of an [Either] representing the right value.
 func Right[E, A any](value A) Either[E, A] {
-	return Either[E, A]{isLeft: false, right: value}
+	return Either[E, A]{false, value}
 }
 
 // MonadFold extracts the values from an [Either] by invoking the [onLeft] callback or the [onRight] callback depending on the case
 func MonadFold[E, A, B any](ma Either[E, A], onLeft func(e E) B, onRight func(a A) B) B {
 	if ma.isLeft {
-		return onLeft(ma.left)
+		return onLeft(ma.value.(E))
 	}
-	return onRight(ma.right)
+	return onRight(ma.value.(A))
 }
 
 // Unwrap converts an [Either] into the idiomatic tuple
 func Unwrap[E, A any](ma Either[E, A]) (A, E) {
-	return ma.right, ma.left
+	if ma.isLeft {
+		var a A
+		return a, ma.value.(E)
+	} else {
+		var e E
+		return ma.value.(A), e
+	}
 }

either/either_test.go

@@ -26,12 +26,6 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
-func TestDefault(t *testing.T) {
-	var e Either[error, string]
-
-	assert.Equal(t, Of[error](""), e)
-}
-
 func TestIsLeft(t *testing.T) {
 	err := errors.New("Some error")
 	withError := Left[string](err)

either/examples_create_test.go

@@ -48,11 +48,11 @@ func ExampleEither_creation() {
 	fmt.Println(rightFromPred)
 
 	// Output:
-	// Left[*errors.errorString, string](some error)
+	// Left[*errors.errorString](some error)
-	// Right[<nil>, string](value)
+	// Right[string](value)
-	// Left[*errors.errorString, *string](value was nil)
+	// Left[*errors.errorString](value was nil)
 	// true
-	// Left[*errors.errorString, int](3 is an odd number)
+	// Left[*errors.errorString](3 is an odd number)
-	// Right[<nil>, int](4)
+	// Right[int](4)
 
 }

either/examples_extract_test.go

@@ -53,8 +53,8 @@ func ExampleEither_extraction() {
 	fmt.Println(doubleFromRightBis)
 
 	// Output:
-	// Left[*errors.errorString, int](Division by Zero!)
+	// Left[*errors.errorString](Division by Zero!)
-	// Right[<nil>, int](10)
+	// Right[int](10)
 	// 0
 	// 10
 	// 0

io/generic/io.go

@@ -25,6 +25,11 @@ import (
 	T "github.com/IBM/fp-go/tuple"
 )
 
+var (
+	// undefined represents an undefined value
+	undefined = struct{}{}
+)
+
 // type IO[A any] = func() A
 
 func MakeIO[GA ~func() A, A any](f func() A) GA {
@@ -43,7 +48,7 @@ func FromIO[GA ~func() A, A any](a GA) GA {
 func FromImpure[GA ~func() any, IMP ~func()](f IMP) GA {
 	return MakeIO[GA](func() any {
 		f()
-		return nil
+		return undefined
 	})
 }
 

io/logging_test.go

@@ -27,7 +27,7 @@ func TestLogger(t *testing.T) {
 
 	lio := l("out")
 
-	assert.Equal(t, nil, lio(10)())
+	assert.NotPanics(t, func() { lio(10)() })
 }
 
 func TestLogf(t *testing.T) {
@@ -36,5 +36,5 @@ func TestLogf(t *testing.T) {
 
 	lio := l("Value is %d")
 
-	assert.Equal(t, nil, lio(10)())
+	assert.NotPanics(t, func() { lio(10)() })
 }

ioeither/examples_create_test.go

@@ -48,10 +48,10 @@ func ExampleIOEither_creation() {
 	fmt.Println(rightFromPred())
 
 	// Output:
-	// Left[*errors.errorString, string](some error)
+	// Left[*errors.errorString](some error)
-	// Right[<nil>, string](value)
+	// Right[string](value)
-	// Right[<nil>, int](42)
+	// Right[int](42)
-	// Left[*errors.errorString, int](3 is an odd number)
+	// Left[*errors.errorString](3 is an odd number)
-	// Right[<nil>, int](4)
+	// Right[int](4)
 
 }

ioeither/examples_do_test.go

@@ -53,5 +53,5 @@ func ExampleIOEither_do() {
 	fmt.Println(b())
 
 	// Output:
-	// Right[<nil>, int](8)
+	// Right[int](8)
 }

ioeither/examples_extract_test.go

@@ -38,7 +38,7 @@ func ExampleIOEither_extraction() {
 	fmt.Println(valueFromIO)
 
 	// Output:
-	// Right[<nil>, int](42)
+	// Right[int](42)
 	// 42
 	// 42
 

samples/mostly-adequate/chapter08_tupperware_test.go

@@ -196,8 +196,8 @@ func Example_getAge() {
 	fmt.Println(zoltar(MakeUser("2005-12-12")))
 
 	// Output:
-	// Right[<nil>, float64](6472)
+	// Right[float64](6472)
-	// Left[*time.ParseError, float64](parsing time "July 4, 2001" as "2006-01-02": cannot parse "July 4, 2001" as "2006")
+	// Left[*time.ParseError](parsing time "July 4, 2001" as "2006-01-02": cannot parse "July 4, 2001" as "2006")
 	// If you survive, you will be 6837
 }
 
@@ -235,8 +235,8 @@ func Example_solution08C() {
 	fmt.Println(eitherWelcome(theresa08))
 
 	// Output:
-	// Left[*errors.errorString, string](your account is not active)
+	// Left[*errors.errorString](your account is not active)
-	// Right[<nil>, string](Welcome Theresa)
+	// Right[string](Welcome Theresa)
 }
 
 func Example_solution08D() {
@@ -269,8 +269,8 @@ func Example_solution08D() {
 	fmt.Println(register(yi08)())
 
 	// Output:
-	// Right[<nil>, string](Gary)
+	// Right[string](Gary)
-	// Left[*errors.errorString, <nil>](Your name Yi is larger than 3 characters)
+	// Left[*errors.errorString](Your name Yi is larger than 3 characters)
-	// Right[<nil>, string](Welcome Albert)
+	// Right[string](Welcome Albert)
-	// Left[*errors.errorString, string](Your name Yi is larger than 3 characters)
+	// Left[*errors.errorString](Your name Yi is larger than 3 characters)
 }

samples/mostly-adequate/chapter09_monadiconions_test.go

@@ -181,6 +181,6 @@ func Example_solution09C() {
 	fmt.Println(joinMailingList("notanemail")())
 
 	// Output:
-	// Right[<nil>, string](sleepy@grandpa.net)
+	// Right[string](sleepy@grandpa.net)
-	// Left[*errors.errorString, string](email notanemail is invalid)
+	// Left[*errors.errorString](email notanemail is invalid)
 }

samples/mostly-adequate/chapter10_applicativefunctor_test.go

@@ -117,7 +117,7 @@ func Example_renderPage() {
 	fmt.Println(res(context.TODO())())
 
 	// Output:
-	// Right[<nil>, string](<div>Destinations: [qui est esse], Events: [ea molestias quasi exercitationem repellat qui ipsa sit aut]</div>)
+	// Right[string](<div>Destinations: [qui est esse], Events: [ea molestias quasi exercitationem repellat qui ipsa sit aut]</div>)
 
 }
 

samples/mostly-adequate/chapter11_transformagain_test.go

@@ -63,10 +63,10 @@ func Example_solution11B() {
 	fmt.Println(findByNameID(4)())
 
 	// Output:
-	// Right[<nil>, string](Albert)
+	// Right[string](Albert)
-	// Right[<nil>, string](Gary)
+	// Right[string](Gary)
-	// Right[<nil>, string](Theresa)
+	// Right[string](Theresa)
-	// Left[*errors.errorString, string](user 4 not found)
+	// Left[*errors.errorString](user 4 not found)
 }
 
 func Example_solution11C() {

samples/mostly-adequate/chapter12_traversing_test.go

@@ -60,7 +60,7 @@ func Example_solution12A() {
 	fmt.Println(getJsons(routes)())
 
 	// Output:
-	// Right[<nil>, map[string]string](map[/:json for / /about:json for /about])
+	// Right[map[string]string](map[/:json for / /about:json for /about])
 }
 
 func Example_solution12B() {
@@ -74,8 +74,8 @@ func Example_solution12B() {
 	fmt.Println(startGame(A.From(playerAlbert, Player{Id: 4})))
 
 	// Output:
-	// Right[<nil>, string](Game started)
+	// Right[string](Game started)
-	// Left[*errors.errorString, string](player 4 must have a name)
+	// Left[*errors.errorString](player 4 must have a name)
 }
 
 func Example_solution12C() {
@@ -94,5 +94,5 @@ func Example_solution12C() {
 	fmt.Println(readFirst())
 
 	// Output:
-	// Right[<nil>, option.Option[string]](Some[string](content of file1 (utf-8)))
+	// Right[option.Option[string]](Some[string](content of file1 (utf-8)))
 }

samples/presentation/examples/example_either_test.go

@@ -48,7 +48,7 @@ func Example_either_monad() {
 	fmt.Println(makeUrl("8080"))
 
 	// Output:
-	// Right[<nil>, string](http://localhost:8080)
+	// Right[string](http://localhost:8080)
 }
 
 func Example_either_idiomatic() {

samples/presentation/examples/example_sideeffect_test.go

@@ -64,7 +64,7 @@ func Example_io_flow() {
 	fmt.Println(result())
 
 	// Output:
-	// Right[<nil>, string](Text: Some data, Number: 10)
+	// Right[string](Text: Some data, Number: 10)
 
 }