Warning - this is old stuff: Gecode/R has been quite inactive since 2008. Most of the code is old and depends on old versions of e.g. Ruby and Gecode.
Website: http://gecoder.org
Gecode/R is a Ruby interface to the Gecode constraint programming library. Gecode/R is intended for people with no previous experience of constraint programming, aiming to be easy to pick up and use.
See Gecode::Mixin to get started.
Gecode/R requires Gecode 2.2.0, which can be downloaded from http://www.gecode.org/download.html. You can either install it yourself, or install a gem that installs it for you.
There are two gems. The first includes only Gecode/R, and assumes that you have installed Gecode yourself. The second includes both Gecode/R and Gecode. If you use Windows then you're recommended to use the second one, even though you already have Gecode, as the other one does not come in a pre-compiled variant.
Gecode/R only:
gem install gecoder
Gecode/R and Gecode:
gem install gecoder-with-gecode
rake gem
gem install pkg/gecoder-1.x.x.gem
gecode.so might have another extension depending on which platform it's
generated on (replace the extension in the following commands with whatever
extension it's given).
cd ext
ruby extconf.rb
make
mv gecode.so ../lib/
rake specs