Consequence

Gem Version

Simple monad implementation with clear and consistent syntax.

Usage

require 'consequence'

Foo = Class.new(Consequence::Monad)
Bar = Class.new(Consequence::Monad)

compare   = ->(v, m) { m == Foo[0] ? Foo[1] : Bar[v] }
transform = ->(v, m) { m == Foo[1] ? 10 : 3 }
validate  = ->(v) { v > 4 ? Bar[v] : Foo[v] }
increment = ->(v) { v + 1 }

react = ->(v, m) { @side_effect = v ** 2 if m.is_a?(Bar) }
log   = ->(v) { @side_effect = @side_effect.to_s }

result = Foo[0] >>
         compare >>   # Foo[1]
         transform >> # Foo[10]
         validate >>  # Bar[10]
         increment >> # Bar[11]
         :next << react << log

p result        # Bar[12]
p @side_effect  # "144"

Operations

  • >> - Chains a proc with the result being passed along. If the result is not a Monad, it is wrapped up in one.

  • << - The supplied proc is applied with the result being ignored and the unchanged Monad is passed down the chain.

If the proc accepts one argument, it is passed only the value of the Monad. If it accepts two values, it is passed both the value and the Monad.

Before being called, the proc have their #to_proc method called. This allows a Symbol to be passed in, whose #to_proc method sends the symbol as a message to the value of the Monad.

Types

Success & Failure

A Success monad wraps up all exceptions in a Failed monad and a Failed monad ignores all chained methods. This allows all possible failures in a long process to be dealt with at the end.

Something & Nothing

A Something monad wraps up a nil result in a Nothing monad and a Nothing monad ignores all chained methods. This prevents MissingMethod errors from trying to be call a method on nil.

More to come...

Installation

Add this line to your application's Gemfile:

gem 'consequence'

Contributing

  1. Fork it ( https://github.com/[my-github-username]/consequence/fork )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request