Prelude – a functional library for Ruby

Prelude is a library of Haskell-style operations written in Ruby with the goal of enabling higher-order functions and monads.

The general idea is that functional programming provides many benefits, which are not directly available in Ruby out of the box. This library will, hopefully, provide an infrastructure for the use of most Haskell’s functional idioms. It will also facilitate a more or less direct port to Ruby of algorithms and data structures already developed by functional community.

Project home is at, here is the API. Feel free to provide financial support for the hosting site.


The latest library version can be downloaded from


Please use the following:

  • forums on Rubyforge for general discussions,
  • trackers to submit bugs or feature requests
  • to contact the authors, send mail to prelude rubyforge org


Prelude library is released under the Lesser GPL license