fix: add flap to Reader

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

README.md

@@ -14,6 +14,8 @@ go get github.com/IBM/fp-go
 
 Refer to the [samples](./samples/).
 
+Find API documentation [here](https://pkg.go.dev/github.com/IBM/fp-go)
+
 ## Design Goal
 
 This library aims to provide a set of data types and functions that make it easy and fun to write maintainable and testable code in golang. It encourages the following patterns:
@@ -192,3 +194,14 @@ this would be the completely generic method signature for all possible monads. I
 This FP library addresses this by introducing the HKTs as individual types, e.g. `HKT[A]` would be represented as a new generic type `HKTA`. This loses the correlation to the type `A` but allows to implement generic algorithms, at the price of readability.
 
 For that reason these implementations are kept in the `internal` package. These are meant to be used by the library itself or by extensions, not by end users.
+
+## Map/Ap/Flap
+
+The following table lists the relationship between some selected operators
+
+| Opertator | Parameter        | Monad           | Result   |
+| --------  | ---------------- | --------------- | -------- |
+| Map       | `func(A) B`      | `HKT[A]`        | `HKT[B]` |
+| Chain     | `func(A) HKT[B]` | `HKT[A]` | `HKT[B]` |
+| Ap        | `HKT[A]`         | `HKT[func(A)B]` | `HKT[B]` |
+| Flap      | `A`              | `HKT[func(A)B]` | `HKT[B]` |

context/readerioeither/generic/reader.go

@@ -664,3 +664,11 @@ func LeftReaderIO[
 	A any](ma GRIOE) GRIOEA {
 	return RIE.LeftReaderIO[GRIOEA](ma)
 }
+
+func MonadFlap[GREAB ~func(context.Context) GEAB, GREB ~func(context.Context) GEB, GEAB ~func() E.Either[error, func(A) B], GEB ~func() E.Either[error, B], B, A any](fab GREAB, a A) GREB {
+	return RIE.MonadFlap[GREAB, GREB](fab, a)
+}
+
+func Flap[GREAB ~func(context.Context) GEAB, GREB ~func(context.Context) GEB, GEAB ~func() E.Either[error, func(A) B], GEB ~func() E.Either[error, B], B, A any](a A) func(GREAB) GREB {
+	return RIE.Flap[GREAB, GREB](a)
+}

context/readerioeither/reader.go

@@ -250,3 +250,11 @@ func RightReaderIO[A any](ma RIO.ReaderIO[A]) ReaderIOEither[A] {
 func LeftReaderIO[A any](ma RIO.ReaderIO[error]) ReaderIOEither[A] {
 	return G.LeftReaderIO[ReaderIOEither[A]](ma)
 }
+
+func MonadFlap[B, A any](fab ReaderIOEither[func(A) B], a A) ReaderIOEither[B] {
+	return G.MonadFlap[ReaderIOEither[func(A) B], ReaderIOEither[B]](fab, a)
+}
+
+func Flap[B, A any](a A) func(ReaderIOEither[func(A) B]) ReaderIOEither[B] {
+	return G.Flap[ReaderIOEither[func(A) B], ReaderIOEither[B]](a)
+}

ioeither/generic/ioeither.go

@@ -25,6 +25,7 @@ import (
 	"github.com/IBM/fp-go/internal/eithert"
 	FE "github.com/IBM/fp-go/internal/fromeither"
 	FI "github.com/IBM/fp-go/internal/fromio"
+	FC "github.com/IBM/fp-go/internal/functor"
 	IO "github.com/IBM/fp-go/io/generic"
 	O "github.com/IBM/fp-go/option"
 )
@@ -304,3 +305,11 @@ func MonadAlt[LAZY ~func() GIOA, GIOA ~func() ET.Either[E, A], E, A any](first G
 func Alt[LAZY ~func() GIOA, GIOA ~func() ET.Either[E, A], E, A any](second LAZY) func(GIOA) GIOA {
 	return F.Bind2nd(MonadAlt[LAZY], second)
 }
+
+func MonadFlap[GEAB ~func() ET.Either[E, func(A) B], GEB ~func() ET.Either[E, B], E, B, A any](fab GEAB, a A) GEB {
+	return FC.MonadFlap(MonadMap[GEAB, GEB], fab, a)
+}
+
+func Flap[GEAB ~func() ET.Either[E, func(A) B], GEB ~func() ET.Either[E, B], E, B, A any](a A) func(GEAB) GEB {
+	return FC.Flap(MonadMap[GEAB, GEB], a)
+}

ioeither/ioeither.go

@@ -231,3 +231,11 @@ func MonadAlt[E, A any](first IOEither[E, A], second L.Lazy[IOEither[E, A]]) IOE
 func Alt[E, A any](second L.Lazy[IOEither[E, A]]) func(IOEither[E, A]) IOEither[E, A] {
 	return G.Alt(second)
 }
+
+func MonadFlap[E, B, A any](fab IOEither[E, func(A) B], a A) IOEither[E, B] {
+	return G.MonadFlap[IOEither[E, func(A) B], IOEither[E, B]](fab, a)
+}
+
+func Flap[E, B, A any](a A) func(IOEither[E, func(A) B]) IOEither[E, B] {
+	return G.Flap[IOEither[E, func(A) B], IOEither[E, B]](a)
+}

readerioeither/generic/reader.go

@@ -24,6 +24,7 @@ import (
 	FIO "github.com/IBM/fp-go/internal/fromio"
 	FIOE "github.com/IBM/fp-go/internal/fromioeither"
 	FR "github.com/IBM/fp-go/internal/fromreader"
+	FC "github.com/IBM/fp-go/internal/functor"
 	IOE "github.com/IBM/fp-go/ioeither/generic"
 	O "github.com/IBM/fp-go/option"
 	RD "github.com/IBM/fp-go/reader/generic"
@@ -431,3 +432,11 @@ func Memoize[
 	GEA ~func(R) GIOA, GIOA ~func() ET.Either[E, A], R, E, A any](rdr GEA) GEA {
 	return G.Memoize[GEA](rdr)
 }
+
+func MonadFlap[GREAB ~func(R) GEAB, GREB ~func(R) GEB, GEAB ~func() ET.Either[E, func(A) B], GEB ~func() ET.Either[E, B], R, E, B, A any](fab GREAB, a A) GREB {
+	return FC.MonadFlap(MonadMap[GREAB, GREB], fab, a)
+}
+
+func Flap[GREAB ~func(R) GEAB, GREB ~func(R) GEB, GEAB ~func() ET.Either[E, func(A) B], GEB ~func() ET.Either[E, B], R, E, B, A any](a A) func(GREAB) GREB {
+	return FC.Flap(MonadMap[GREAB, GREB], a)
+}

readerioeither/reader.go

@@ -272,3 +272,11 @@ func Memoize[
 	R, E, A any](rdr ReaderIOEither[R, E, A]) ReaderIOEither[R, E, A] {
 	return G.Memoize[ReaderIOEither[R, E, A]](rdr)
 }
+
+func MonadFlap[R, E, B, A any](fab ReaderIOEither[R, E, func(A) B], a A) ReaderIOEither[R, E, B] {
+	return G.MonadFlap[ReaderIOEither[R, E, func(A) B], ReaderIOEither[R, E, B]](fab, a)
+}
+
+func Flap[R, E, B, A any](a A) func(ReaderIOEither[R, E, func(A) B]) ReaderIOEither[R, E, B] {
+	return G.Flap[ReaderIOEither[R, E, func(A) B], ReaderIOEither[R, E, B]](a)
+}