bleu.rb : BLEU implementation, also per-sentence-BLEU
      dag.rb : implementation of a directed acyclic graph and various algorithms
 fileutil.rb : file utilities
  grammar.rb : classes to model grammars (mostly for translation grammars)
       hg.rb : data structures and algorithms (viterbi currently) for hypergraphs
     misc.rb : misc. stuff (e.g. monkey patches for Array and String)
semirings.rb : semirings (used in dags.rb)