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

Examples

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

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

nothing.upcase                         # => #<Monads::Nothing>
nothing.upcase.split.unwrap([])        # => []
nothing.bind { |v| just }              # => #<Monads::Nothing>
nothing.fmap { |v| v.gsub(/\w/, "*") } # => #<Monads::Nothing>
Maybe.unit(nothing).join               # => #<Monads::Nothing>

Why this gem

This gem is heavily inspired by the following monads implementations:

• Monadic
• Monads

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, unit, 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