Project

ruby-monads

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ruby-monadsguillaumeboudon/ruby-monadsHomepageDocumentationSource CodeBug TrackerWiki
Simple and minimalist ruby implementation of some common monads
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 Popularity
Downloads
5,138
Stars
1
Forks
0
Watchers
1
 Releases
Current version
1.0.0
Total releases
4
First release
2020-08-07
Latest release
2024-11-21
 Development
Primary Language
Ruby
Licenses
MIT
Average date of last 50 commits
2021-08-14
Reverse Dependencies
0

 Dependencies

Development

cutest
~> 1.2, >= 1.2.3
rubocop
~> 1, >= 1.68
standard
~> 1.42, >= 1.42.1
 Project Readme

ruby-monads

These are some Ruby implementations of some common monads.

Usage

If you don't already have it installed:

gem install ruby-monads

As these are just some new abstractions, just include it:

require "monads"

include Monads

Monads

Maybe

The maybe monad returns one of the following classes, wether it wraps a value or not:

  • Maybe.wrap(42) returns an instance of Just wrapping the 42 value
  • Maybe.wrap(nil) returns an instance of Nothing wrapping no value

Examples

Maybe.wrap("Hello, World!")                                # => #<Monads::Just @value="Hello, World!">
Maybe.wrap(nil)                                            # => #<Monads::Nothing>

Maybe.wrap("Hello, World!").upcase                         # => #<Monads::Just @value="HELLO, WORLD!">
Maybe.wrap("Hello, World!").upcase.split.unwrap([])        # => ["HELLO,", "WORLD!"]
Maybe.wrap("Hello, World!").bind { |v| Maybe.wrap(nil) }   # => #<Monads::Nothing>
Maybe.wrap("Hello, World!").fmap { |v| v.gsub(/\w/, "*") } # => #<Monads::Just @value="*****, *****!">
Maybe.wrap(Maybe.wrap("Hello, World!")).join               # => #<Monads::Just @value="Hello, World!">

Maybe.wrap(nil).upcase                                     # => #<Monads::Nothing>
Maybe.wrap(nil).upcase.split.unwrap([])                    # => []
Maybe.wrap(nil).bind { |v| Maybe.wrap("Hello, World!") }   # => #<Monads::Maybe.wrap(nil)>
Maybe.wrap(nil).fmap { |v| v.gsub(/\w/, "*") }             # => #<Monads::Nothing>
Maybe.wrap(Maybe.wrap(nil)).join                           # => #<Monads::Nothing>

Result

The result monad returns one of the following classes, wether it wraps an error or not:

  • Result.wrap(42) returns an instance of Success wrapping the 42 value
  • Result.wrap(StandardError.new) returns an instance of Failure wrapping the given error

Examples

Result.wrap("Hello, World!")             # => #<Monads::Success @value="Hello, World!">
Result.wrap(StandardError.new("Wrong!")) # => #<Monads::Failure @value=#<StandardError: Wrong!>>

Result
  .wrap("Hello, World!")                 # => #<Monads::Success @value="Hello, World!">
  .upcase                                # => #<Monads::Success @value="HELLO, WORLD!">
  .even                                  # => #<Monads::Failure @value=#<NoMethodError: undefined method `even?' for "HELLO, WORLD!":String>>
  .split                                 # => #<Monads::Failure @value=#<NoMethodError: undefined method `even?' for "HELLO, WORLD!":String>>
  .unwrap("default")                     # "default"

Why this gem

This gem is heavily inspired by the following monads implementations:

These gems, and many others are really great, and it was very instructive to learn about this topic in my beloved language. However, after reading a lot of implementations and articles, I had a clear opinion of how I wanted it:

  • Minimalist: as simple an lightweight as possible
  • Respectful of uses: respectful of the usual terms (Monad (functional programming)), like Maybe, wrap, bind, join, etc.
  • Vanilla Ruby syntax: I love some of the abstractions I discovered (>= operator, Just(value) syntax). However, I also love vanilla Ruby. So, I wanted to target new methods and abstractions, not new syntaxes comming from other languages.

Tests

Test suite uses cutest. You can execute it with:

make