Just forgot one reference, kent Ref: http://www.cs.indiana.edu/~dyb/papers/fpp-abstract.html http://riss.keris.or.kr:8080/pubs/articles/proceedings/pldi/231379/p108-burger/p108-burger.pdf http://tosca.cs.unict.it/~vs/LaP/haskell/haskell98-library-report/numeric.html