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reader

An implementation of Reader Monad in Moonbit

reader
monad
reader monad
DI
dependency injection
moon add colmugx/reader@0.3.0
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Author
Version
0.3.0
License
Apache-2.0
Repository
Last updated
7 months ago
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40
README

#colmugx/reader

MoonBit implementation of the Reader Monad pattern.

The Reader Monad allows you to easily manage and access a shared environment (like configuration or dependencies) throughout a computation without explicitly passing it around.

#Installation

moon add colmugx/reader

#License

This project appears to be licensed under the MIT License (based on the LICENSE file). Please refer to the LICENSE file for full details.

#
Reader

source
pub struct Reader[Env, A] {
  // private fields
}

#
Reader::bind

source
fn[Env, A, B] Reader::bind(reader : Reader[Env, A], f : (A) -> Reader[Env, B]) -> Reader[Env, B]

Chains two reader computations by applying a function to the result of the first reader to produce a second reader computation.

Parameters:

  • reader : The first reader computation that produces a value of type A.
  • f : A function that takes the result of the first reader and returns a new reader computation of type B.

Returns a new reader that represents the sequential composition of the two computations.

Example:

///|
test "Reader::bind" {
  let reader1 = Reader::pure(5)
  let reader2 = reader1.bind(fn { x => Reader::pure(x * 2) })
  inspect!(reader2.run(0), content="10")
}

#
Reader::local_

source
fn[Env, A] Reader::local_(reader : Reader[Env, A], modifier : (Env) -> Env) -> Reader[Env, A]

Executes a reader computation with a modified environment.

Parameters:

  • reader : A Reader computation that produces a value of type A.
  • modifier : A function that transforms the environment before it's passed to the reader computation.

Returns a new reader that will run the original computation with the modified environment.

Example:

///|
test "Reader::local_" {
  let reader = Reader::new(fn { env => env * 2 })
  let modified = reader.local_(fn { env => env + 1 })
  inspect!(modified.run(5), content="12")
}

#
Reader::map

source
fn[Env, A, B] Reader::map(reader : Reader[Env, A], f : (A) -> B) -> Reader[Env, B]

#
Reader::pure

source
fn[Env, A] Reader::pure(x : A) -> Reader[Env, A]

Creates a new Reader that ignores the environment and always returns a constant value.

Parameters:

  • x : The value to be returned by the reader.

Generic Parameters:

  • Env : The type of environment (which will be ignored).
  • A : The type of the value to be returned.

Returns a new Reader that always produces the given value regardless of the environment.

Example:

test "Reader::pure" {
  let reader = Reader::pure("constant")
  inspect(reader.run(42), content="constant")
}

#
Reader::run

source
fn[Env, A] Reader::run(reader : Reader[Env, A], config : Env) -> A

Executes a reader computation with the given environment.

Parameters:

  • reader : A Reader that contains the computation to be executed.
  • environment : The environment value to be provided to the computation.

Returns the result of running the reader computation with the given environment.

Example:

///|
test "Reader::run" {
  let reader = Reader::new(fn { env => env + 1 })
  inspect!(reader.run(41), content="42")
}

#
ask

source
fn[Env] ask() -> Reader[Env, Env]

Creates a Reader that simply returns the environment itself.

Generic Parameters:

  • Env: The type of the environment.

Returns a reader computation that produces the environment when run.

Example:

test "ask" {
  let reader = ask()
  inspect(reader.run("hello"), content="hello")
}

#
asks

source
fn[Env, A] asks(f : (Env) -> A) -> Reader[Env, A]

Creates a Reader that transforms the environment using a given function.

Parameters:

  • f : A function that takes an environment of type Env and produces a value of type A. This function will be applied to the environment when the reader is run.

Returns a new Reader that will apply the given function to the environment.

Example:

///|
test "asks" {
  let reader = asks(fn { env => env + 1 })
  inspect!(reader.run(41), content="42")
}

Source Files

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