writer

Documentation

Index

• func Ap[B, A, W any](s S.Semigroup[W]) func(Writer[W, A]) func(Writer[W, func(A) B]) Writer[W, B]
• func ApS[S1, S2, T, W any](s S.Semigroup[W]) ...
• func Bind[S1, S2, T, W any](s S.Semigroup[W]) ...
• func BindTo[W, S1, T any](setter func(T) S1) func(Writer[W, T]) Writer[W, S1]
• func Censor[FCT ~func(W) W, W, A any](f FCT) func(Writer[W, A]) Writer[W, A]
• func Chain[A, B, W any](s S.Semigroup[W]) func(func(A) Writer[W, B]) func(Writer[W, A]) Writer[W, B]
• func ChainFirst[FCT ~func(A) Writer[W, B], W, A, B any](s S.Semigroup[W]) func(FCT) func(Writer[W, A]) Writer[W, A]
• func Do[S, W any](m M.Monoid[W]) func(S) Writer[W, S]
• func Eq[W, A any](w EQ.Eq[W], a EQ.Eq[A]) EQ.Eq[Writer[W, A]]
• func Evaluate[W, A any](fa Writer[W, A]) A
• func Execute[W, A any](fa Writer[W, A]) W
• func Flatten[W, A any](s S.Semigroup[W]) func(Writer[W, Writer[W, A]]) Writer[W, A]
• func FromStrictEquals[W, A comparable]() EQ.Eq[Writer[W, A]]
• func Let[W, S1, S2, T any](setter func(T) func(S1) S2, f func(S1) T) func(Writer[W, S1]) Writer[W, S2]
• func LetTo[W, S1, S2, T any](setter func(T) func(S1) S2, b T) func(Writer[W, S1]) Writer[W, S2]
• func Listens[FCT ~func(W) B, W, A, B any](f FCT) func(Writer[W, A]) Writer[W, T.Tuple2[A, B]]
• func Map[W any, FCT ~func(A) B, A, B any](f FCT) func(Writer[W, A]) Writer[W, B]
• func MonadAp[B, A, W any](s S.Semigroup[W]) func(Writer[W, func(A) B], Writer[W, A]) Writer[W, B]
• func MonadChain[FCT ~func(A) Writer[W, B], W, A, B any](s S.Semigroup[W]) func(Writer[W, A], FCT) Writer[W, B]
• func MonadChainFirst[FCT ~func(A) Writer[W, B], W, A, B any](s S.Semigroup[W]) func(Writer[W, A], FCT) Writer[W, A]
• func Of[A, W any](m M.Monoid[W]) func(A) Writer[W, A]
• type Writer
  • func Listen[W, A any](fa Writer[W, A]) Writer[W, T.Tuple2[A, W]]
  • func MonadCensor[FCT ~func(W) W, W, A any](fa Writer[W, A], f FCT) Writer[W, A]
  • func MonadListens[FCT ~func(W) B, W, A, B any](fa Writer[W, A], f FCT) Writer[W, T.Tuple2[A, B]]
  • func MonadMap[FCT ~func(A) B, W, A, B any](fa Writer[W, A], f FCT) Writer[W, B]
  • func Pass[W, A any](fa Writer[W, T.Tuple2[A, EM.Endomorphism[W]]]) Writer[W, A]

Examples

• Writer (Logging)

Functions

func Ap

func Ap[B, A, W any](s S.Semigroup[W]) func(Writer[W, A]) func(Writer[W, func(A) B]) Writer[W, B]

func ApS

func ApS[S1, S2, T, W any](s S.Semigroup[W]) func(
	setter func(T) func(S1) S2,
	fa Writer[W, T],
) func(Writer[W, S1]) Writer[W, S2]

ApS attaches a value to a context [S1] to produce a context [S2] by considering the context and the value concurrently

func Bind

func Bind[S1, S2, T, W any](s S.Semigroup[W]) func(
	setter func(T) func(S1) S2,
	f func(S1) Writer[W, T],
) func(Writer[W, S1]) Writer[W, S2]

Bind attaches the result of a computation to a context [S1] to produce a context [S2]

func BindTo

func BindTo[W, S1, T any](
	setter func(T) S1,
) func(Writer[W, T]) Writer[W, S1]

BindTo initializes a new state [S1] from a value [T]

func Censor

func Censor[FCT ~func(W) W, W, A any](f FCT) func(Writer[W, A]) Writer[W, A]

Censor modifies the final accumulator value by applying a function

func Chain

func Chain[A, B, W any](s S.Semigroup[W]) func(func(A) Writer[W, B]) func(Writer[W, A]) Writer[W, B]

func ChainFirst

func ChainFirst[FCT ~func(A) Writer[W, B], W, A, B any](s S.Semigroup[W]) func(FCT) func(Writer[W, A]) Writer[W, A]

func Do

func Do[S, W any](m M.Monoid[W]) func(S) Writer[W, S]

Bind creates an empty context of type [S] to be used with the Bind operation

func Eq

func Eq[W, A any](w EQ.Eq[W], a EQ.Eq[A]) EQ.Eq[Writer[W, A]]

Constructs an equal predicate for a Writer

func Evaluate

func Evaluate[W, A any](fa Writer[W, A]) A

Evaluate extracts the value

func Execute

func Execute[W, A any](fa Writer[W, A]) W

Execute extracts the accumulator

func Flatten

func Flatten[W, A any](s S.Semigroup[W]) func(Writer[W, Writer[W, A]]) Writer[W, A]

func FromStrictEquals

func FromStrictEquals[W, A comparable]() EQ.Eq[Writer[W, A]]

FromStrictEquals constructs an [EQ.Eq] from the canonical comparison function

func Let

func Let[W, S1, S2, T any](
	setter func(T) func(S1) S2,
	f func(S1) T,
) func(Writer[W, S1]) Writer[W, S2]

Let attaches the result of a computation to a context [S1] to produce a context [S2]

func LetTo

func LetTo[W, S1, S2, T any](
	setter func(T) func(S1) S2,
	b T,
) func(Writer[W, S1]) Writer[W, S2]

LetTo attaches the a value to a context [S1] to produce a context [S2]

func Listens

func Listens[FCT ~func(W) B, W, A, B any](f FCT) func(Writer[W, A]) Writer[W, T.Tuple2[A, B]]

Listens projects a value from modifications made to the accumulator during an action

func Map

func Map[W any, FCT ~func(A) B, A, B any](f FCT) func(Writer[W, A]) Writer[W, B]

func MonadAp

func MonadAp[B, A, W any](s S.Semigroup[W]) func(Writer[W, func(A) B], Writer[W, A]) Writer[W, B]

func MonadChain

func MonadChain[FCT ~func(A) Writer[W, B], W, A, B any](s S.Semigroup[W]) func(Writer[W, A], FCT) Writer[W, B]

func MonadChainFirst

func MonadChainFirst[FCT ~func(A) Writer[W, B], W, A, B any](s S.Semigroup[W]) func(Writer[W, A], FCT) Writer[W, A]

func Of

func Of[A, W any](m M.Monoid[W]) func(A) Writer[W, A]

Types

type Writer

type Writer[W, A any] IO.IO[T.Tuple2[A, W]]

Example (Logging)

package main

import (
	"fmt"

	A "github.com/IBM/fp-go/array"
	F "github.com/IBM/fp-go/function"
	M "github.com/IBM/fp-go/monoid"
	T "github.com/IBM/fp-go/tuple"
)

func doubleAndLog(data int) Writer[[]string, int] {
	return func() T.Tuple2[int, []string] {
		result := data * 2
		return T.MakeTuple2(result, A.Of(fmt.Sprintf("Doubled %d -> %d", data, result)))
	}
}

func main() {

	m := A.Monoid[string]()
	s := M.ToSemigroup(m)

	res := F.Pipe3(
		10,
		Of[int](m),
		Chain[int, int](s)(doubleAndLog),
		Chain[int, int](s)(doubleAndLog),
	)

	fmt.Println(res())

}

Output:

Tuple2[int, []string](40, [Doubled 10 -> 20 Doubled 20 -> 40])

func Listen

func Listen[W, A any](fa Writer[W, A]) Writer[W, T.Tuple2[A, W]]

Listen modifies the result to include the changes to the accumulator

func MonadCensor

func MonadCensor[FCT ~func(W) W, W, A any](fa Writer[W, A], f FCT) Writer[W, A]

MonadCensor modifies the final accumulator value by applying a function

func MonadListens

func MonadListens[FCT ~func(W) B, W, A, B any](fa Writer[W, A], f FCT) Writer[W, T.Tuple2[A, B]]

MonadListens projects a value from modifications made to the accumulator during an action

func MonadMap

func MonadMap[FCT ~func(A) B, W, A, B any](fa Writer[W, A], f FCT) Writer[W, B]

func Pass

func Pass[W, A any](fa Writer[W, T.Tuple2[A, EM.Endomorphism[W]]]) Writer[W, A]

Pass applies the returned function to the accumulator