monads v1.0.0
monads
Monads for Crystal.
Inspired by https://github.com/dry-rb/dry-monads
Installation
Add this to your application's shard.yml
:
dependencies:
monads:
github: alex-lairan/monads
Usage
require "monads"
Many monads exist.
Maybe(T)
The Maybe monad helps to avoid nil
and chain instructions.
There are two kinds of Maybe, Just
and Nothing
.
Just(T)
This is just a value.
Monads::Just.new(5)
Nothing(T)
This is an absence of value.
Monads::Nothing(Int32).new
Either(E, T)
The Either monad helps to manage errors at the end of the chain of instructions.
There are two kinds of Either, Right
and Left
.
Right(T)
This is just a value.
Monads::Right.new("Hello world")
Left(E)
This is an error.
Monads::Left.new("User password is incorrect")
List(T)
The List monad helps to manipulate an Array like a monad.
Monads::List[1, 6, 4, 2]
head
head
returns the first element wrapped within a Maybe
.
tail
tail
returns the list without the first element.
Try(T)
The Try
monad is a layer between Object Oriented Exception and Fuctional Programming Monads. It can be transformed into a Maybe
or an Either
.
Task(T)
The Task
monad is a parallelized Try
monad. Its goal is to use the power of fibers with monads.
How to use a monad ?
Monads have some methods which help to chain instructions.
Try
and Task
monads should be translated into a Maybe(T)
or an Either(Exception, T)
one.
fmap
The fmap
procedure modify the internal value of a monad.
This doesn't affect Nothing
and Left
monads.
Example:
value = Monads::Just.new(5)
.fmap(->(x : Int32) { x.to_s })
.fmap(->(x : String) { x + "12" })
.fmap(->(x : String) { x.to_i })
.value!
value.should eq(512)
bind
The bind
procedure allows to create a whole new monad from the internal data of another.
This doesn't affect Nothing
and Left
monads.
Example:
value = Monads::Just.new(5)
.bind(->(x : Int32) { Monads::Try(Int32).new(-> { x / 0}).to_maybe })
value.should eq(Monads::Nothing(Int32).new)
Development
Clone then let's go, no special requirements.
Contributing
- Fork it (https://github.com/alex-lairan/monads/fork)
- Create your feature branch (
git checkout -b my-new-feature
) - Commit your changes (
git commit -am 'Add some feature'
) - Push to the branch (
git push origin my-new-feature
) - Create a new Pull Request
Contributors
- alex-lairan Alexandre Lairan - creator, maintainer
- moba1 moba - maintainer
monads
- 47
- 3
- 0
- 9
- 1
- about 2 years ago
- October 14, 2018
MIT License
Sat, 21 Dec 2024 22:23:06 GMT