Reference · Core Type

ReaderIO

Combine dependency injection (Reader) with lazy side effects (IO). ReaderIO[C, A] for effectful computations with dependencies.

Packagegithub.com/IBM/fp-go/v2/readerio

TypeMonad (func(C) IO[A])

01

Overview

type_definition.go

package readerio

// ReaderIO combines Reader and IO
type ReaderIO[C, A any] = Reader[C, IO[A]]
// Which expands to: func(C) func() A

02

Core API

Constructors

Function	Signature	Description
Of	func Of[C, A any](value A) ReaderIO[C, A]	Wrap pure value
Ask	func Ask[C any]() ReaderIO[C, C]	Access context
Asks	func Asks[C, A any](f func(C) A) ReaderIO[C, A]	Access and transform context
FromIO	func FromIO[C, A any](io IO[A]) ReaderIO[C, A]	Lift IO to ReaderIO
FromReader	func FromReader[C, A any](r Reader[C, A]) ReaderIO[C, A]	Lift Reader to ReaderIO

Transformations

Function	Signature	Description
Map	func Map[C, A, B any](f func(A) B) func(ReaderIO[C, A]) ReaderIO[C, B]	Transform result
Chain	func Chain[C, A, B any](f func(A) ReaderIO[C, B]) func(ReaderIO[C, A]) ReaderIO[C, B]	Sequence operations

03

Usage Examples

Basic Usage

basic.go

package main

import (
  RIO "github.com/IBM/fp-go/v2/readerio"
  IO "github.com/IBM/fp-go/v2/io"
)

type Dependencies struct {
  Logger *log.Logger
}

func logMessage(msg string) RIO.ReaderIO[Dependencies, unit.Unit] {
  return RIO.Ask[Dependencies, *log.Logger](func(deps Dependencies) *log.Logger {
      return deps.Logger
  }).Chain(func(logger *log.Logger) RIO.ReaderIO[Dependencies, unit.Unit] {
      return RIO.FromIO(IO.FromImpure(func() {
          logger.Println(msg)
      }))
  })
}

func main() {
  deps := Dependencies{Logger: log.New(os.Stdout, "", 0)}
  logMessage("Hello, World!")(deps)()
}