mo

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README

mo - Monads

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🦄 samber/mo brings monads and popular FP abstractions to Go projects. samber/mo uses the recent Go 1.18+ Generics.

Inspired by:

  • Scala
  • Rust
  • FP-TS

See also:

  • samber/lo: A Lodash-style Go library based on Go 1.18+ Generics
  • samber/do: A dependency injection toolkit based on Go 1.18+ Generics

Why this name?

I love short name for such utility library. This name is similar to "Monad Go" and no Go package currently uses this name.

💡 Features

We currently support the following data types:

  • Option[T] (Maybe)
  • Result[T]
  • Either[A, B]
  • Future[T]
  • IO[T]
  • IOEither[T]
  • Task[T]
  • TaskEither[T]
  • State[S, A]

🚀 Install

go get github.com/samber/mo@v1

This library is v1 and follows SemVer strictly.

No breaking changes will be made to exported APIs before v2.0.0.

💡 Quick start

You can import mo using:

import (
    "github.com/samber/mo"
)

Then use one of the helpers below:

option1 := mo.Some(42)
// Some(42)

option1.
    FlatMap(func (value int) Option[int] {
        return Some(value*2)
    }).
    FlatMap(func (value int) Option[int] {
        return Some(value%2)
    }).
    FlatMap(func (value int) Option[int] {
        return Some(value+21)
    }).
    OrElse(1234)
// 21

option2 := mo.None[int]()
// None

option2.OrElse(1234)
// 1234

option3 := option1.Match(
    func(i int) (int, bool) {
        // when value is present
        return i * 2, true
    },
    func() (int, bool) {
        // when value is absent
        return 0, false
    },
)
// Some(42)

More examples in documentation.

🤠 Documentation and examples

GoDoc: https://godoc.org/github.com/samber/mo

Option[T any]

Option is a container for an optional value of type T. If value exists, Option is of type Some. If the value is absent, Option is of type None.

Constructors:

  • mo.Some() doc
  • mo.None() doc
  • mo.TupleToOption() doc

Methods:

Result[T any]

Result respresent a result of an action having one of the following output: success or failure. An instance of Result is an instance of either Ok or Err. It could be compared to Either[error, T].

Constructors:

  • mo.Ok() doc
  • mo.Err() doc
  • mo.TupleToResult() doc

Methods:

Either[L any, R any]

Either respresents a value of 2 possible types. An instance of Either is an instance of either A or B.

Constructors:

  • mo.Left() doc
  • mo.Right() doc

Methods:

  • .IsLeft() doc
  • .IsRight() doc
  • .Left() doc
  • .Right() doc
  • .MustLeft() doc
  • .MustRight() doc
  • .LeftOrElse() doc
  • .RightOrElse() doc
  • .LeftOrEmpty() doc
  • .RightOrEmpty() doc
  • .Swap() doc
  • .ForEach() doc
  • .Match() doc
  • .MapLeft() doc
  • .MapRight() doc
Future[T any]

Future represents a value which may or may not currently be available, but will be available at some point, or an exception if that value could not be made available.

Constructors:

  • mo.NewFuture() doc

Methods:

IO[T any]

IO represents a non-deterministic synchronous computation that can cause side effects, yields a value of type R and never fails.

Constructors:

  • mo.NewIO() doc
  • mo.NewIO1() doc
  • mo.NewIO2() doc
  • mo.NewIO3() doc
  • mo.NewIO4() doc
  • mo.NewIO5() doc

Methods:

IOEither[T any]

IO represents a non-deterministic synchronous computation that can cause side effects, yields a value of type R and can fail.

Constructors:

  • mo.NewIOEither() doc
  • mo.NewIOEither1() doc
  • mo.NewIOEither2() doc
  • mo.NewIOEither3() doc
  • mo.NewIOEither4() doc
  • mo.NewIOEither5() doc

Methods:

Task[T any]

Task represents a non-deterministic asynchronous computation that can cause side effects, yields a value of type R and never fails.

Constructors:

  • mo.NewTask() doc
  • mo.NewTask1() doc
  • mo.NewTask2() doc
  • mo.NewTask3() doc
  • mo.NewTask4() doc
  • mo.NewTask5() doc
  • mo.NewTaskFromIO() doc
  • mo.NewTaskFromIO1() doc
  • mo.NewTaskFromIO2() doc
  • mo.NewTaskFromIO3() doc
  • mo.NewTaskFromIO4() doc
  • mo.NewTaskFromIO5() doc

Methods:

TaskEither[T any]

TaskEither represents a non-deterministic asynchronous computation that can cause side effects, yields a value of type R and can fail.

Constructors:

  • mo.NewTaskEither() doc
  • mo.NewTaskEitherFromIOEither() doc

Methods:

State[S any, A any]

State represents a function (S) -> (A, S), where S is state, A is result.

Constructors:

  • mo.NewState() doc
  • mo.ReturnState() doc

Methods:

🛩 Benchmark

// @TODO

This library does not use reflect package. We don't expect overhead.

🤝 Contributing

Don't hesitate ;)

With Docker
docker-compose run --rm dev
Without Docker
# Install some dev dependencies
make tools

# Run tests
make test
# or
make watch-test

👤 Authors

  • Samuel Berthe

💫 Show your support

Give a ⭐️ if this project helped you!

support us

📝 License

Copyright © 2022 Samuel Berthe.

This project is MIT licensed.

Documentation

Index

Examples

Constants

This section is empty.

Variables

This section is empty.

Functions

This section is empty.

Types

type Either 

type Either[L any, R any] struct {
	// contains filtered or unexported fields
}

Either respresents a value of 2 possible types. An instance of Either is an instance of either A or B.

func Left 

func Left[L any, R any](value L) Either[L, R]

Left builds the left side of the Either struct, as opposed to the Right side.

Example 
left := Left[string, int]("hello")
result1 := left.LeftOrElse("world")
result2 := left.RightOrElse(1234)

fmt.Println(result1, result2)

Output:

hello 1234

func Right[L any, R any](value R) Either[L, R]

Right builds the right side of the Either struct, as opposed to the Left side.

Example 
right := Right[string, int](42)
result1 := right.LeftOrElse("world")
result2 := right.RightOrElse(1234)

fmt.Println(result1, result2)

Output:

world 42

func (Either[L, R]) ForEach 

func (e Either[L, R]) ForEach(leftCb func(L), rightCb func(R))

ForEach executes the given side-effecting function, depending of value is Left or Right.

func (Either[L, R]) IsLeft 

func (e Either[L, R]) IsLeft() bool

IsLeft returns true if Either is an instance of Left.

Example (Left) 
left := Left[string, int]("hello")
result := left.IsLeft()

fmt.Println(result)

Output:

true
Example (Right) 
right := Right[string, int](42)
result := right.IsLeft()

fmt.Println(result)

Output:

false

func (Either[L, R]) IsRight 

func (e Either[L, R]) IsRight() bool

IsRight returns true if Either is an instance of Right.

Example (Left) 
left := Left[string, int]("hello")
result := left.IsRight()

fmt.Println(result)

Output:

false
Example (Right) 
right := Right[string, int](42)
result := right.IsRight()

fmt.Println(result)

Output:

true

func (Either[L, R]) Left 

func (e Either[L, R]) Left() (L, bool)

Left returns left value of a Either struct.

Example (Left) 
left := Left[string, int]("hello")
result, ok := left.Left()

fmt.Println(result)
fmt.Println(ok)

Output:

hello
true
Example (Right) 
right := Right[string, int](42)
result, ok := right.Left()

fmt.Println(result)
fmt.Println(ok)

Output:

false

func (Either[L, R]) LeftOrElse 

func (e Either[L, R]) LeftOrElse(fallback L) L

LeftOrElse returns left value of a Either struct or fallback.

Example (Left) 
left := Left[string, int]("hello")
result := left.LeftOrElse("world")

fmt.Println(result)

Output:

hello
Example (Right) 
right := Right[string, int](42)
result := right.LeftOrElse("world")

fmt.Println(result)

Output:

world

func (Either[L, R]) LeftOrEmpty 

func (e Either[L, R]) LeftOrEmpty() L

LeftOrEmpty returns left value of a Either struct or empty value.

Example (Left) 
left := Left[string, int]("hello")
result := left.LeftOrEmpty()

fmt.Println(result)

Output:

hello
Example (Right) 
right := Right[string, int](42)
result := right.LeftOrEmpty()

fmt.Println(result)

Output:

func (Either[L, R]) MapLeft 

func (e Either[L, R]) MapLeft(mapper func(L) Either[L, R]) Either[L, R]

MapLeft executes the given function, if Either is of type Left, and returns result.

Example (Left) 
left := Left[string, int]("hello")
result := left.MapLeft(
	func(s string) Either[string, int] {
		return Right[string, int](1234)
	},
)
result1, ok1 := result.Left()
result2, ok2 := result.Right()

fmt.Println(result1)
fmt.Println(ok1)
fmt.Println(result2)
fmt.Println(ok2)

Output:

false
1234
true
Example (Right) 
right := Right[string, int](42)
result := right.MapLeft(
	func(s string) Either[string, int] {
		return Left[string, int]("world")
	},
)
result1, ok1 := result.Left()
result2, ok2 := result.Right()

fmt.Println(result1)
fmt.Println(ok1)
fmt.Println(result2)
fmt.Println(ok2)

Output:

false
42
true

func (Either[L, R]) MapRight 

func (e Either[L, R]) MapRight(mapper func(R) Either[L, R]) Either[L, R]

MapRight executes the given function, if Either is of type Right, and returns result.

Example (Left) 
left := Left[string, int]("hello")
result := left.MapRight(
	func(i int) Either[string, int] {
		return Right[string, int](1234)
	},
)
result1, ok1 := result.Left()
result2, ok2 := result.Right()

fmt.Println(result1)
fmt.Println(ok1)
fmt.Println(result2)
fmt.Println(ok2)

Output:

hello
true
0
false
Example (Right) 
right := Right[string, int](42)
result := right.MapRight(
	func(i int) Either[string, int] {
		return Right[string, int](1234)
	},
)
result1, ok1 := result.Left()
result2, ok2 := result.Right()

fmt.Println(result1)
fmt.Println(ok1)
fmt.Println(result2)
fmt.Println(ok2)

Output:

false
1234
true

func (Either[L, R]) Match 

func (e Either[L, R]) Match(onLeft func(L) Either[L, R], onRight func(R) Either[L, R]) Either[L, R]

Match executes the given function, depending of value is Left or Right, and returns result.

Example (Left) 
left := Left[string, int]("hello")
result := left.Match(
	func(s string) Either[string, int] {
		return Right[string, int](1234)
	},
	func(i int) Either[string, int] {
		return Right[string, int](i * 42)
	},
)
result1, ok1 := result.Left()
result2, ok2 := result.Right()

fmt.Println(result1)
fmt.Println(ok1)
fmt.Println(result2)
fmt.Println(ok2)

Output:

false
1234
true
Example (Right) 
right := Right[string, int](42)
result := right.Match(
	func(s string) Either[string, int] {
		return Left[string, int]("world")
	},
	func(i int) Either[string, int] {
		return Left[string, int]("foobar")
	},
)
result1, ok1 := result.Left()
result2, ok2 := result.Right()

fmt.Println(result1)
fmt.Println(ok1)
fmt.Println(result2)
fmt.Println(ok2)

Output:

foobar
true
0
false

func (Either[L, R]) MustLeft 

func (e Either[L, R]) MustLeft() L

MustLeft returns left value of a Either struct or panics.

Example (Left) 
left := Left[string, int]("hello")
result := left.MustLeft()

fmt.Println(result)

Output:

hello

func (Either[L, R]) MustRight 

func (e Either[L, R]) MustRight() R

MustRight returns right value of a Either struct or panics.

Example (Right) 
right := Right[string, int](42)
result := right.MustRight()

fmt.Println(result)

Output:

42

func (Either[L, R]) Right 

func (e Either[L, R]) Right() (R, bool)

Right returns right value of a Either struct.

Example (Left) 
left := Left[string, int]("hello")
result, ok := left.Right()

fmt.Println(result)
fmt.Println(ok)

Output:

0
false
Example (Right) 
right := Right[string, int](42)
result, ok := right.Right()

fmt.Println(result)
fmt.Println(ok)

Output:

42
true

func (Either[L, R]) RightOrElse 

func (e Either[L, R]) RightOrElse(fallback R) R

RightOrElse returns right value of a Either struct or fallback.

Example (Left) 
left := Left[string, int]("hello")
result := left.RightOrElse(1234)

fmt.Println(result)

Output:

1234
Example (Right) 
right := Right[string, int](42)
result := right.RightOrElse(1234)

fmt.Println(result)

Output:

42

func (Either[L, R]) RightOrEmpty 

func (e Either[L, R]) RightOrEmpty() R

RightOrEmpty returns right value of a Either struct or empty value.

Example (Left) 
left := Left[string, int]("hello")
result := left.RightOrEmpty()

fmt.Println(result)

Output:

0
Example (Right) 
right := Right[string, int](42)
result := right.RightOrEmpty()

fmt.Println(result)

Output:

42

func (Either[L, R]) Swap 

func (e Either[L, R]) Swap() Either[R, L]

Swap returns the left value in Right and vice versa.

Example (Left) 
left := Left[string, int]("hello")
right := left.Swap()
result1, ok1 := right.Left()
result2, ok2 := right.Right()

fmt.Println(result1)
fmt.Println(ok1)
fmt.Println(result2)
fmt.Println(ok2)

Output:

0
false
hello
true
Example (Right) 
right := Right[string, int](42)
left := right.Swap()
result1, ok1 := left.Left()
result2, ok2 := left.Right()

fmt.Println(result1)
fmt.Println(ok1)
fmt.Println(result2)
fmt.Println(ok2)
// 42
// true
//
// false

Output:

type Future 

type Future[T any] struct {
	// contains filtered or unexported fields
}

Future represents a value which may or may not currently be available, but will be available at some point, or an exception if that value could not be made available.

func NewFuture 

func NewFuture[T any](cb func(resolve func(T), reject func(error))) *Future[T]

NewFuture instanciate a new future.

Example (Reject) 
value, err := NewFuture(func(resolve func(string), reject func(error)) {
	reject(fmt.Errorf("failure"))
}).Collect()

fmt.Println(value)
fmt.Println(err)

Output:


failure
Example (Resolve) 
value, err := NewFuture(func(resolve func(string), reject func(error)) {
	resolve("foobar")
}).Collect()

fmt.Println(value)
fmt.Println(err)

Output:

foobar
<nil>

func (*Future[T]) Cancel 

func (f *Future[T]) Cancel()

Cancel cancels the Future chain.

Example (Reject) 
NewFuture(func(resolve func(string), reject func(error)) {
	reject(fmt.Errorf("failure"))
}).Cancel()

Output:
Example (Resolve) 
NewFuture(func(resolve func(string), reject func(error)) {
	resolve("foobar")
}).Cancel()

Output:

func (*Future[T]) Catch 

func (f *Future[T]) Catch(cb func(error) (T, error)) *Future[T]

Catch is called when Future is rejected. It returns a new Future.

Example (Reject) 
result := NewFuture(func(resolve func(string), reject func(error)) {
	reject(fmt.Errorf("failure"))
}).Catch(func(err error) (string, error) {
	return "foobar", nil
}).Result()

fmt.Println(result.OrEmpty())
fmt.Println(result.Error())

Output:

foobar
<nil>
Example (Resolve) 
result := NewFuture(func(resolve func(string), reject func(error)) {
	resolve("foobar")
}).Catch(func(err error) (string, error) {
	return "baz", nil
}).Result()

fmt.Println(result.OrEmpty())
fmt.Println(result.Error())

Output:

foobar
<nil>

func (*Future[T]) Collect 

func (f *Future[T]) Collect() (T, error)

Collect awaits and return result of the Future.

Example (Reject) 
value, err := NewFuture(func(resolve func(string), reject func(error)) {
	reject(fmt.Errorf("failure"))
}).Collect()

fmt.Println(value)
fmt.Println(err)

Output:


failure
Example (Resolve) 
value, err := NewFuture(func(resolve func(string), reject func(error)) {
	resolve("foobar")
}).Collect()

fmt.Println(value)
fmt.Println(err)

Output:

foobar
<nil>

func (*Future[T]) Either 

func (f *Future[T]) Either() Either[error, T]

Result wraps Collect and returns a Result.

func (*Future[T]) Finally 

func (f *Future[T]) Finally(cb func(T, error) (T, error)) *Future[T]

Finally is called when Future is processed either resolved or rejected. It returns a new Future.

Example (Reject) 
result := NewFuture(func(resolve func(string), reject func(error)) {
	reject(fmt.Errorf("failure"))
}).Finally(func(value string, err error) (string, error) {
	return "foobar", nil
}).Result()

fmt.Println(result.OrEmpty())
fmt.Println(result.Error())

Output:

foobar
<nil>
Example (Resolve) 
result := NewFuture(func(resolve func(string), reject func(error)) {
	resolve("foobar")
}).Finally(func(value string, err error) (string, error) {
	return "baz", nil
}).Result()

fmt.Println(result.OrEmpty())
fmt.Println(result.Error())

Output:

baz
<nil>

func (*Future[T]) Result 

func (f *Future[T]) Result() Result[T]

Result wraps Collect and returns a Result.

Example (Reject) 
result := NewFuture(func(resolve func(string), reject func(error)) {
	reject(fmt.Errorf("failure"))
}).Result()

fmt.Println(result.OrEmpty())
fmt.Println(result.Error())

Output:


failure
Example (Resolve) 
result := NewFuture(func(resolve func(string), reject func(error)) {
	resolve("foobar")
}).Result()

fmt.Println(result.OrEmpty())
fmt.Println(result.Error())

Output:

foobar
<nil>

func (*Future[T]) Then 

func (f *Future[T]) Then(cb func(T) (T, error)) *Future[T]

Catch is called when Future is resolved. It returns a new Future.

Example (Reject) 
result := NewFuture(func(resolve func(string), reject func(error)) {
	reject(fmt.Errorf("failure"))
}).Then(func(s string) (string, error) {
	return "foobar", nil
}).Result()

fmt.Println(result.OrEmpty())
fmt.Println(result.Error())

Output:


failure
Example (Resolve) 
result := NewFuture(func(resolve func(string), reject func(error)) {
	resolve("foobar")
}).Then(func(s string) (string, error) {
	return "baz", nil
}).Result()

fmt.Println(result.OrEmpty())
fmt.Println(result.Error())

Output:

baz
<nil>

type IO 

type IO[R any] struct {
	// contains filtered or unexported fields
}

IO represents a non-deterministic synchronous computation that can cause side effects, yields a value of type `R` and never fails.

Example 
io := NewIO(func() int {
	return time.Now().Year()
})

result1 := io.Run()
result2 := io.Run()
result3 := io.Run()

fmt.Println(result1)
fmt.Println(result2)
fmt.Println(result3)

Output:

2022
2022
2022

func NewIO 

func NewIO[R any](f f0[R]) IO[R]

NewIO instanciates a new IO.

func (IO[R]) Run 

func (io IO[R]) Run() R

Run execute the non-deterministic synchronous computation, with side effect.

type IO1 

type IO1[R any, A any] struct {
	// contains filtered or unexported fields
}

IO1 represents a non-deterministic synchronous computation that can cause side effects, yields a value of type `R` and never fails.

func NewIO1 

func NewIO1[R any, A any](f f1[R, A]) IO1[R, A]

NewIO1 instanciates a new IO1.

func (IO1[R, A]) Run 

func (io IO1[R, A]) Run(a A) R

Run execute the non-deterministic synchronous computation, with side effect.

type IO2 

type IO2[R any, A any, B any] struct {
	// contains filtered or unexported fields
}

IO2 represents a non-deterministic synchronous computation that can cause side effects, yields a value of type `R` and never fails.

func NewIO2 

func NewIO2[R any, A any, B any](f f2[R, A, B]) IO2[R, A, B]

NewIO2 instanciates a new IO2.

func (IO2[R, A, B]) Run 

func (io IO2[R, A, B]) Run(a A, b B) R

Run execute the non-deterministic synchronous computation, with side effect.

type IO3 

type IO3[R any, A any, B any, C any] struct {
	// contains filtered or unexported fields
}

IO3 represents a non-deterministic synchronous computation that can cause side effects, yields a value of type `R` and never fails.

func NewIO3 

func NewIO3[R any, A any, B any, C any](f f3[R, A, B, C]) IO3[R, A, B, C]

NewIO3 instanciates a new IO3.

func (IO3[R, A, B, C]) Run 

func (io IO3[R, A, B, C]) Run(a A, b B, c C) R

Run execute the non-deterministic synchronous computation, with side effect.

type IO4 

type IO4[R any, A any, B any, C any, D any] struct {
	// contains filtered or unexported fields
}

IO4 represents a non-deterministic synchronous computation that can cause side effects, yields a value of type `R` and never fails.

func NewIO4 

func NewIO4[R any, A any, B any, C any, D any](f f4[R, A, B, C, D]) IO4[R, A, B, C, D]

NewIO4 instanciates a new IO4.

func (IO4[R, A, B, C, D]) Run 

func (io IO4[R, A, B, C, D]) Run(a A, b B, c C, d D) R

Run execute the non-deterministic synchronous computation, with side effect.

type IO5 

type IO5[R any, A any, B any, C any, D any, E any] struct {
	// contains filtered or unexported fields
}

IO5 represents a non-deterministic synchronous computation that can cause side effects, yields a value of type `R` and never fails.

func NewIO5 

func NewIO5[R any, A any, B any, C any, D any, E any](f f5[R, A, B, C, D, E]) IO5[R, A, B, C, D, E]

NewIO5 instanciates a new IO5.

func (IO5[R, A, B, C, D, E]) Run 

func (io IO5[R, A, B, C, D, E]) Run(a A, b B, c C, d D, e E) R

Run execute the non-deterministic synchronous computation, with side effect.

type IOEither 

type IOEither[R any] struct {
	// contains filtered or unexported fields
}

IO represents a non-deterministic synchronous computation that can cause side effects, yields a value of type `R` and can fail.

func NewIOEither 

func NewIOEither[R any](f fe0[R]) IOEither[R]

NewIOEither instanciates a new IO.

func (IOEither[R]) Run 

func (io IOEither[R]) Run() Either[error, R]

Run execute the non-deterministic synchronous computation, with side effect.

type IOEither1 

type IOEither1[R any, A any] struct {
	// contains filtered or unexported fields
}

IO1 represents a non-deterministic synchronous computation that can cause side effects, yields a value of type `R` and can fail.

Example 
io := NewIOEither1(func(path string) (bool, error) {
	_, err := os.Stat(path)

	if errors.Is(err, os.ErrNotExist) {
		return false, nil
	} else if err != nil {
		// other errors
		return false, err
	}

	return true, nil
})

either1 := io.Run("./io_either.go")
either2 := io.Run("./foo_bar.go")

exist1, _ := either1.Right()
exist2, _ := either2.Right()

fmt.Println(exist1)
fmt.Println(exist2)

Output:

true
false

func NewIOEither1 

func NewIOEither1[R any, A any](f fe1[R, A]) IOEither1[R, A]

NewIOEither1 instanciates a new IO1.

func (IOEither1[R, A]) Run 

func (io IOEither1[R, A]) Run(a A) Either[error, R]

Run execute the non-deterministic synchronous computation, with side effect.

type IOEither2 

type IOEither2[R any, A any, B any] struct {
	// contains filtered or unexported fields
}

IO2 represents a non-deterministic synchronous computation that can cause side effects, yields a value of type `R` and can fail.

func NewIOEither2 

func NewIOEither2[R any, A any, B any](f fe2[R, A, B]) IOEither2[R, A, B]

NewIOEither2 instanciates a new IO2.

func (IOEither2[R, A, B]) Run 

func (io IOEither2[R, A, B]) Run(a A, b B) Either[error, R]

Run execute the non-deterministic synchronous computation, with side effect.

type IOEither3 

type IOEither3[R any, A any, B any, C any] struct {
	// contains filtered or unexported fields
}

IO3 represents a non-deterministic synchronous computation that can cause side effects, yields a value of type `R` and can fail.

func NewIOEither3 

func NewIOEither3[R any, A any, B any, C any](f fe3[R, A, B, C]) IOEither3[R, A, B, C]

NewIOEither3 instanciates a new IO3.

func (IOEither3[R, A, B, C]) Run 

func (io IOEither3[R, A, B, C]) Run(a A, b B, c C) Either[error, R]

Run execute the non-deterministic synchronous computation, with side effect.

type IOEither4 

type IOEither4[R any, A any, B any, C any, D any] struct {
	// contains filtered or unexported fields
}

IO4 represents a non-deterministic synchronous computation that can cause side effects, yields a value of type `R` and can fail.

func NewIOEither4 

func NewIOEither4[R any, A any, B any, C any, D any](f fe4[R, A, B, C, D]) IOEither4[R, A, B, C, D]

NewIOEither4 instanciates a new IO4.

func (IOEither4[R, A, B, C, D]) Run 

func (io IOEither4[R, A, B, C, D]) Run(a A, b B, c C, d D) Either[error, R]

Run execute the non-deterministic synchronous computation, with side effect.

type IOEither5 

type IOEither5[R any, A any, B any, C any, D any, E any] struct {
	// contains filtered or unexported fields
}

IO5 represents a non-deterministic synchronous computation that can cause side effects, yields a value of type `R` and can fail.

func NewIOEither5 

func NewIOEither5[R any, A any, B any, C any, D any, E any](f fe5[R, A, B, C, D, E]) IOEither5[R, A, B, C, D, E]

NewIOEither5 instanciates a new IO5.

func (IOEither5[R, A, B, C, D, E]) Run 

func (io IOEither5[R, A, B, C, D, E]) Run(a A, b B, c C, d D, e E) Either[error, R]

Run execute the non-deterministic synchronous computation, with side effect.

type Option 

type Option[T any] struct {
	// contains filtered or unexported fields
}

Option is a container for an optional value of type T. If value exists, Option is of type Some. If the value is absent, Option is of type None.

Example (None) 
none := None[int]()
result := none.OrElse(1234)

fmt.Println(result)

Output:

1234
Example (Some) 
some := Some(42)
result := some.OrElse(1234)

fmt.Println(result)

Output:

42

func None 

func None[T any]() Option[T]

None builds an Option when value is absent.

Example 
none := None[int]()
result := none.OrElse(1234)

fmt.Println(result)

Output:

1234

func Some 

func Some[T any](value T) Option[T]

Some builds an Option when value is present.

Example 
some := Some(42)
result := some.OrElse(1234)

fmt.Println(result)

Output:

42

func TupleToOption 

func TupleToOption[T any](value T, ok bool) Option[T]
Example 
m := map[string]int{
	"foo": 21,
	"bar": 42,
	"baz": 84,
}

value, ok := m["hello world"]

none := TupleToOption(value, ok)
result := none.OrElse(1234)

fmt.Println(result)

Output:

1234

func (Option[T]) FlatMap 

func (o Option[T]) FlatMap(mapper func(value T) Option[T]) Option[T]

FlatMap executes the mapper function if value is present or returns None if absent.

Example (None) 
none := None[int]()
result := none.FlatMap(func(i int) Option[int] {
	return Some(21)
})

fmt.Println(result.IsPresent(), result.OrEmpty())

Output:

false 0
Example (Some) 
some := Some(42)
result := some.FlatMap(func(i int) Option[int] {
	return Some(21)
})

fmt.Println(result.IsPresent(), result.OrEmpty())

Output:

true 21

func (Option[T]) ForEach 

func (o Option[T]) ForEach(onValue func(value T))

ForEach executes the given side-effecting function of value is present.

func (Option[T]) Get 

func (o Option[T]) Get() (T, bool)

Get returns value and presence.

Example (None) 
none := None[int]()
result, ok := none.Get()

fmt.Println(result)
fmt.Println(ok)

Output:

0
false
Example (Some) 
some := Some(42)
result, ok := some.Get()

fmt.Println(result)
fmt.Println(ok)

Output:

42
true

func (Option[T]) IsAbsent 

func (o Option[T]) IsAbsent() bool

IsAbsent returns true when value is present.

Example (None) 
none := None[int]()
result := none.IsAbsent()

fmt.Println(result)

Output:

true
Example (Some) 
some := Some(42)
result := some.IsAbsent()

fmt.Println(result)

Output:

false

func (Option[T]) IsPresent 

func (o Option[T]) IsPresent() bool

IsPresent returns true when value is absent.

Example (None) 
none := None[int]()
result := none.IsPresent()

fmt.Println(result)

Output:

false
Example (Some) 
some := Some(42)
result := some.IsPresent()

fmt.Println(result)

Output:

true

func (Option[T]) Map 

func (o Option[T]) Map(mapper func(value T) (T, bool)) Option[T]

Map executes the mapper function if value is present or returns None if absent.

Example (None) 
none := None[int]()
result := none.Map(func(i int) (int, bool) {
	return 1234, true
})

fmt.Println(result.IsPresent(), result.OrEmpty())

Output:

false 0
Example (Some) 
some := Some(42)
result := some.Map(func(i int) (int, bool) {
	return 1234, true
})

fmt.Println(result.IsPresent(), result.OrEmpty())

Output:

true 1234

func (Option[T]) MapNone 

func (o Option[T]) MapNone(mapper func() (T, bool)) Option[T]

MapNone executes the mapper function if value is absent or returns Option.

Example (None) 
none := None[int]()
result := none.MapNone(func() (int, bool) {
	return 1234, true
})

fmt.Println(result.IsPresent(), result.OrEmpty())

Output:

true 1234
Example (Some) 
some := Some(42)
result := some.MapNone(func() (int, bool) {
	return 1234, true
})

fmt.Println(result.IsPresent(), result.OrEmpty())

Output:

true 42

func (Option[T]) Match 

func (o Option[T]) Match(onValue func(value T) (T, bool), onNone func() (T, bool)) Option[T]

Match executes the first function if value is present and second function if absent. It returns a new Option.

Example (None) 
none := None[int]()
result := none.Match(
	func(i int) (int, bool) {
		return 0, false
	},
	func() (int, bool) {
		return 2, true
	},
)

fmt.Println(result.IsPresent(), result.OrEmpty())

Output:

true 2
Example (Some) 
some := Some(42)
result := some.Match(
	func(i int) (int, bool) {
		return 0, false
	},
	func() (int, bool) {
		return 2, true
	},
)

fmt.Println(result.IsPresent(), result.OrEmpty())

Output:

false 0

func (Option[T]) MustGet 

func (o Option[T]) MustGet() T

MustGet returns value if present or panics instead.

Example (Some) 
some := Some(42)
result := some.MustGet()

fmt.Println(result)

Output:

42

func (Option[T]) OrElse 

func (o Option[T]) OrElse(fallback T) T

OrElse returns value if present or default value.

Example (None) 
none := None[int]()
result := none.OrElse(1234)

fmt.Println(result)

Output:

1234
Example (Some) 
some := Some(42)
result := some.OrElse(1234)

fmt.Println(result)

Output:

42

func (Option[T]) OrEmpty 

func (o Option[T]) OrEmpty() T

OrEmpty returns value if present or empty value.

Example (None) 
none := None[int]()
result := none.OrEmpty()

fmt.Println(result)

Output:

0
Example (Some) 
some := Some(42)
result := some.OrEmpty()

fmt.Println(result)

Output:

42

func (Option[T]) Size 

func (o Option[T]) Size() int

Size returns 1 when value is present or 0 instead.

Example (None) 
none := None[int]()
result := none.Size()

fmt.Println(result)

Output:

0
Example (Some) 
some := Some(42)
result := some.Size()

fmt.Println(result)

Output:

1

type Result 

type Result[T any] struct {
	// contains filtered or unexported fields
}

Result respresent a result of an action having one of the following output: success or failure. An instance of Result is an instance of either Ok or Err. It could be compared to `Either[error, T]`.

Example (Err) 
ko := Err[int](err)
result := ko.OrElse(1234)
_err := ko.Error()

fmt.Println(result, _err)

Output:

1234 error
Example (Ok) 
ok := Ok(42)
result := ok.OrElse(1234)
_err := ok.Error()

fmt.Println(result, _err)

Output:

42 <nil>

func Err 

func Err[T any](err error) Result[T]

Err builds a Result when value is invalid.

Example 
ko := Err[int](err)
result := ko.OrElse(1234)
_err := ko.Error()

fmt.Println(result, _err)

Output:

1234 error

func Ok 

func Ok[T any](value T) Result[T]

Ok builds a Result when value is valid.

Example 
ok := Ok(42)
result := ok.OrElse(1234)
_err := ok.Error()

fmt.Println(result, _err)

Output:

42 <nil>

func TupleToResult 

func TupleToResult[T any](value T, err error) Result[T]

TupleToResult convert a pair of T and error into a Result.

Example 
randomFunc := func() (int, error) {
	return 42, err
}

value, _err := randomFunc()

none := TupleToResult(value, _err)
result := none.OrElse(1234)

fmt.Println(result)

Output:

1234

func (Result[T]) Error 

func (r Result[T]) Error() error

Error returns error when value is invalid or nil.

Example (Err) 
ko := Err[int](err)
result := ko.Error()

fmt.Println(result)

Output:

error
Example (Ok) 
ok := Ok(42)
result := ok.Error()

fmt.Println(result)

Output:

<nil>

func (Result[T]) FlatMap 

func (r Result[T]) FlatMap(mapper func(value T) Result[T]) Result[T]

FlatMap executes the mapper function if Result is valid. It returns a new Result.

Example (Err) 
ko := Err[int](err)
result := ko.FlatMap(
	func(i int) Result[int] {
		return Ok(1234)
	},
)

fmt.Println(result.IsError(), result.OrEmpty(), result.Error())

Output:

true 0 error
Example (Ok) 
ok := Ok(42)
result := ok.FlatMap(
	func(i int) Result[int] {
		return Ok(1234)
	},
)

fmt.Println(result.IsError(), result.OrEmpty(), result.Error())

Output:

false 1234 <nil>

func (Result[T]) ForEach 

func (r Result[T]) ForEach(mapper func(value T))

ForEach executes the given side-effecting function if Result is valid.

func (Result[T]) Get 

func (r Result[T]) Get() (T, error)

MustGet returns value and error.

Example (Err) 
ko := Err[int](err)
result, err := ko.Get()

fmt.Println(result)
fmt.Println(err)

Output:

0
error
Example (Ok) 
ok := Ok(42)
result, err := ok.Get()

fmt.Println(result)
fmt.Println(err)

Output:

42
<nil>

func (Result[T]) IsError 

func (r Result[T]) IsError() bool

IsError returns true when value is invalid.

Example (Err) 
ko := Err[int](err)
result := ko.IsError()

fmt.Println(result)

Output:

true
Example (Ok) 
ok := Ok(42)
result := ok.IsError()

fmt.Println(result)

Output:

false

func (Result[T]) IsOk 

func (r Result[T]) IsOk() bool

IsOk returns true when value is valid.

Example (Err) 
ko := Err[int](err)
result := ko.IsOk()

fmt.Println(result)

Output:

false
Example (Ok) 
ok := Ok(42)
result := ok.IsOk()

fmt.Println(result)

Output:

true

func (Result[T]) Map 

func (r Result[T]) Map(mapper func(value T) (T, error)) Result[T]

Map executes the mapper function if Result is valid. It returns a new Result.

Example (Err) 
ko := Err[int](err)
result := ko.Map(
	func(i int) (int, error) {
		return i * 2, nil
	},
)

fmt.Println(result.IsError(), result.OrEmpty(), result.Error())

Output:

true 0 error
Example (Ok) 
ok := Ok(42)
result := ok.Map(
	func(i int) (int, error) {
		return i * 2, nil
	},
)

fmt.Println(result.IsError(), result.OrEmpty(), result.Error())

Output:

false 84 <nil>

func (Result[T]) MapErr 

func (r Result[T]) MapErr(mapper func(error) (T, error)) Result[T]

MapErr executes the mapper function if Result is invalid. It returns a new Result.

Example (Err) 
ko := Err[int](err)
result := ko.MapErr(
	func(_err error) (int, error) {
		return 1234, nil
	},
)

fmt.Println(result.IsError(), result.OrEmpty(), result.Error())

Output:

false 1234 <nil>
Example (Ok) 
ok := Ok(42)
result := ok.MapErr(
	func(_err error) (int, error) {
		return 1234, nil
	},
)

fmt.Println(result.IsError(), result.OrEmpty(), result.Error())

Output:

false 42 <nil>

func (Result[T]) Match 

func (r Result[T]) Match(onSuccess func(value T) (T, error), onError func(err error) (T, error)) Result[T]

Match executes the first function if Result is valid and second function if invalid. It returns a new Result.

Example (Err) 
ko := Err[int](err)
result := ko.Match(
	func(i int) (int, error) {
		return i * 2, nil
	},
	func(err error) (int, error) {
		return 21, nil
	},
)

fmt.Println(result.IsError(), result.OrEmpty(), result.Error())

Output:

false 21 <nil>
Example (Ok) 
ok := Ok(42)
result := ok.Match(
	func(i int) (int, error) {
		return i * 2, nil
	},
	func(err error) (int, error) {
		return 21, nil
	},
)

fmt.Println(result.IsError(), result.OrEmpty(), result.Error())

Output:

false 84 <nil>

func (Result[T]) MustGet 

func (r Result[T]) MustGet() T

MustGet returns value when Result is valid or panics.

Example (Ok) 
ok := Ok(42)
result := ok.MustGet()

fmt.Println(result)

Output:

42

func (Result[T]) OrElse 

func (r Result[T]) OrElse(fallback T) T

OrElse returns value when Result is valid or default value.

Example (Err) 
ko := Err[int](err)
result := ko.OrElse(1234)

fmt.Println(result)

Output:

1234
Example (Ok) 
ok := Ok(42)
result := ok.OrElse(1234)

fmt.Println(result)

Output:

42

func (Result[T]) OrEmpty 

func (r Result[T]) OrEmpty() T

OrEmpty returns value when Result is valid or empty value.

Example (Err) 
ko := Err[int](err)
result := ko.OrEmpty()

fmt.Println(result)

Output:

0
Example (Ok) 
ok := Ok(42)
result := ok.OrEmpty()

fmt.Println(result)

Output:

42

func (Result[T]) ToEither 

func (r Result[T]) ToEither() Either[error, T]

ToEither transforms a Result into an Either type.

Example (Err) 
ko := Err[int](err)
either := ko.ToEither()

err, isLeft := either.Left()
value, isRight := either.Right()

fmt.Println(isLeft, isRight)
fmt.Println(err)
fmt.Println(value)

Output:

true false
error
0
Example (Ok) 
ok := Ok(42)
either := ok.ToEither()

err, isLeft := either.Left()
value, isRight := either.Right()

fmt.Println(isLeft, isRight)
fmt.Println(err)
fmt.Println(value)

Output:

false true
<nil>
42

type State 

type State[S any, A any] struct {
	// contains filtered or unexported fields
}

State represents a function `(S) -> (A, S)`, where `S` is state, `A` is result.

func NewState 

func NewState[S any, A any](f func(state S) (A, S)) State[S, A]

func ReturnState 

func ReturnState[S any, A any](x A) State[S, A]

func (State[S, A]) Get 

func (s State[S, A]) Get() State[S, S]

Get returns the current state.

func (State[S, A]) Modify 

func (s State[S, A]) Modify(f func(state S) S) State[S, A]

Modify the state by applying a function to the current state.

func (State[S, A]) Put 

func (s State[S, A]) Put(state S) State[S, A]

Put set the state.

func (State[S, A]) Run 

func (s State[S, A]) Run(state S) (A, S)

Run executes a computation in the State monad.

type Task 

type Task[R any] struct {
	// contains filtered or unexported fields
}

Task represents a non-deterministic asynchronous computation that can cause side effects, yields a value of type `R` and never fails.

Example 
task := NewTask(func() *Future[int] {
	return NewFuture(func(resolve func(int), reject func(error)) {
		resolve(time.Now().Year())
	})
})

// returns a future
future := task.Run()

// a Task never fail
result, _ := future.Collect()

fmt.Println(result)

Output:

2022

func NewTask 

func NewTask[R any](f ff0[R]) Task[R]

NewTask instanciates a new Task.

func NewTaskFromIO 

func NewTaskFromIO[R any](io IO[R]) Task[R]

NewTaskFromIO instanciates a new Task from an existing IO.

func (Task[R]) Run 

func (t Task[R]) Run() *Future[R]

Run execute the non-deterministic asynchronous computation, with side effect.

type Task1 

type Task1[R any, A any] struct {
	// contains filtered or unexported fields
}

Task1 represents a non-deterministic asynchronous computation that can cause side effects, yields a value of type `R` and never fails.

func NewTask1 

func NewTask1[R any, A any](f ff1[R, A]) Task1[R, A]

NewTask1 instanciates a new Task1.

func NewTaskFromIO1 

func NewTaskFromIO1[R any, A any](io IO1[R, A]) Task1[R, A]

NewTaskFromIO1 instanciates a new Task1 from an existing IO1.

func (Task1[R, A]) Run 

func (t Task1[R, A]) Run(a A) *Future[R]

Run execute the non-deterministic asynchronous computation, with side effect.

type Task2 

type Task2[R any, A any, B any] struct {
	// contains filtered or unexported fields
}

Task2 represents a non-deterministic asynchronous computation that can cause side effects, yields a value of type `R` and never fails.

func NewTask2 

func NewTask2[R any, A any, B any](f ff2[R, A, B]) Task2[R, A, B]

NewTask2 instanciates a new Task2.

func NewTaskFromIO2 

func NewTaskFromIO2[R any, A any, B any](io IO2[R, A, B]) Task2[R, A, B]

NewTaskFromIO2 instanciates a new Task2 from an existing IO2.

func (Task2[R, A, B]) Run 

func (t Task2[R, A, B]) Run(a A, b B) *Future[R]

Run execute the non-deterministic asynchronous computation, with side effect.

type Task3 

type Task3[R any, A any, B any, C any] struct {
	// contains filtered or unexported fields
}

Task3 represents a non-deterministic asynchronous computation that can cause side effects, yields a value of type `R` and never fails.

func NewTask3 

func NewTask3[R any, A any, B any, C any](f ff3[R, A, B, C]) Task3[R, A, B, C]

NewTask3 instanciates a new Task3.

func NewTaskFromIO3 

func NewTaskFromIO3[R any, A any, B any, C any](io IO3[R, A, B, C]) Task3[R, A, B, C]

NewTaskFromIO3 instanciates a new Task3 from an existing IO3.

func (Task3[R, A, B, C]) Run 

func (t Task3[R, A, B, C]) Run(a A, b B, c C) *Future[R]

Run execute the non-deterministic asynchronous computation, with side effect.

type Task4 

type Task4[R any, A any, B any, C any, D any] struct {
	// contains filtered or unexported fields
}

Task4 represents a non-deterministic asynchronous computation that can cause side effects, yields a value of type `R` and never fails.

func NewTask4 

func NewTask4[R any, A any, B any, C any, D any](f ff4[R, A, B, C, D]) Task4[R, A, B, C, D]

NewTask4 instanciates a new Task4.

func NewTaskFromIO4 

func NewTaskFromIO4[R any, A any, B any, C any, D any](io IO4[R, A, B, C, D]) Task4[R, A, B, C, D]

NewTaskFromIO4 instanciates a new Task4 from an existing IO4.

func (Task4[R, A, B, C, D]) Run 

func (t Task4[R, A, B, C, D]) Run(a A, b B, c C, d D) *Future[R]

Run execute the non-deterministic asynchronous computation, with side effect.

type Task5 

type Task5[R any, A any, B any, C any, D any, E any] struct {
	// contains filtered or unexported fields
}

Task5 represents a non-deterministic asynchronous computation that can cause side effects, yields a value of type `R` and never fails.

func NewTask5 

func NewTask5[R any, A any, B any, C any, D any, E any](f ff5[R, A, B, C, D, E]) Task5[R, A, B, C, D, E]

NewTask5 instanciates a new Task5.

func NewTaskFromIO5 

func NewTaskFromIO5[R any, A any, B any, C any, D any, E any](io IO5[R, A, B, C, D, E]) Task5[R, A, B, C, D, E]

NewTaskFromIO5 instanciates a new Task5 from an existing IO5.

func (Task5[R, A, B, C, D, E]) Run 

func (t Task5[R, A, B, C, D, E]) Run(a A, b B, c C, d D, e E) *Future[R]

Run execute the non-deterministic asynchronous computation, with side effect.

type TaskEither 

type TaskEither[R any] struct {
	Task[R]
}

TaskEither represents a non-deterministic asynchronous computation that can cause side effects, yields a value of type `R` and can fail.

func NewTaskEither 

func NewTaskEither[R any](f ff0[R]) TaskEither[R]

NewTaskEither instanciates a new TaskEither.

func NewTaskEitherFromIO 

func NewTaskEitherFromIO[R any](io IO[R]) TaskEither[R]

NewTaskEitherFromIO instanciates a new TaskEither from an existing IO.

func (TaskEither[R]) Match 

func (t TaskEither[R]) Match(onLeft func(error) Either[error, R], onRight func(R) Either[error, R]) Either[error, R]

Match executes the first function if task succeeded and second function if task failed. It returns a new Option.

func (TaskEither[R]) OrElse 

func (t TaskEither[R]) OrElse(fallback R) R

OrElse returns value if task succeeded or default value.

func (TaskEither[R]) ToEither 

func (t TaskEither[R]) ToEither() Either[error, R]

ToTask converts TaskEither to Task

func (TaskEither[R]) ToTask 

func (t TaskEither[R]) ToTask(fallback R) Task[R]

ToTask converts TaskEither to Task

func (TaskEither[R]) TryCatch 

func (t TaskEither[R]) TryCatch(onLeft func(error) Either[error, R], onRight func(R) Either[error, R]) Either[error, R]

TryCatch is an alias to Match

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