= Rumonade[https://rubygems.org/gems/rumonade] Project: github[http://github.com/ms-ati/rumonade] Documentation: rubydoc.info[http://rubydoc.info/gems/rumonade/file/README.rdoc] == A Ruby[http://www.ruby-lang.org] Monad[http://en.wikipedia.org/wiki/Monad_(functional_programming)] Library, Inspired by Scala[http://www.scala-lang.org] Are you working in both the Scala[http://www.scala-lang.org] and Ruby[http://www.ruby-lang.org] worlds, and finding that you miss some of the practical benefits of Scala's monads[http://james-iry.blogspot.com/2007/09/monads-are-elephants-part-1.html] in Ruby? Then Rumonade is for you. The goal of this library is to make the most common and useful Scala monadic idioms available in Ruby via the following classes: * {Rumonade::Option Option} * {Rumonade::ArrayExtensions Array} * {Rumonade::Either Either} * Hash -- _coming_ _soon!_ * (_more_ _TBD_) Syntactic support for scala-like for-comprehensions[http://www.scala-lang.org/node/111] will be implemented as a sequence of calls to #flat_map, #select, etc, modelling Scala's approach[http://stackoverflow.com/questions/3754089/scala-for-comprehension/3754568#3754568]. Support for an all_catch[http://www.scala-lang.org/archives/downloads/distrib/files/nightly/docs/library/scala/util/control/Exception$.html] idiom will be implemented to turn blocks which might throw exceptions into Option or Either results. If this proves useful (and a good fit for Ruby), then more narrow functional catchers can be implemented as well. == Usage Using Option, one can transform _possibly_ _nil_ values in a _functional_ fashion, which can increase clarity while eliminating opportunities for bugs: def format_date_in_march(time_or_date_or_nil) Option(time_or_date_or_nil). # wraps possibly-nil value in an Option monad (Some or None) map(&:to_date). # transforms a contained Time value into a Date value select {|d| d.month == 3}. # filters out non-matching Date values (Some becomes None) map(&:to_s). # transforms a contained Date value into a String value map {|s| s.gsub('-', '')}. # transforms a contained String value by removing '-' get_or_else("not in march!") # returns the contained value, or the alternative if None end format_date_in_march(nil) # => "not in march!" format_date_in_march(Time.parse('2009-01-01 01:02')) # => "not in march!" format_date_in_march(Time.parse('2011-03-21 12:34')) # => "20110321" Note: * each step of the chained computations above are functionally isolated * the value can notionally _start_ as nil, or _become_ nil during a computation, without effecting any other chained computations (_more_ _examples_ _coming_ _soon_...) == Approach There have been many[http://moonbase.rydia.net/mental/writings/programming/monads-in-ruby/00introduction.html] posts[http://pretheory.wordpress.com/2008/02/14/the-maybe-monad-in-ruby/] and[http://www.valuedlessons.com/2008/01/monads-in-ruby-with-nice-syntax.html] discussions[http://stackoverflow.com/questions/2709361/monad-equivalent-in-ruby] about monads in Ruby, which have sparked a number of approaches. Rumonade wants to be a practical drop-in Monad solution that will fit well into the Ruby world. The priorities for Rumonade are: 1. Practical usability in day-to-day Ruby * don't mess up normal idioms of the language (e.g., Hash#map) * don't slow down normal idioms of the language (e.g., Array#map) 2. Rubyish-ness of usage * Monad is a mix-in, requiring methods self.unit and #bind be implemented by target classes * Prefer blocks to lambda/Procs where possible 3. Equivalent idioms to Scala where possible == Status This code is in a very early state, but the Option monad is already present. Please try it out, and let me know what you think!