DrHylo: A tool for deriving hylomorphisms

DrHylo

This cabal package can be installed with:

$ cabal install DrHylo

For a manual install, execute:

$ runhaskell Setup.lhs configure
$ runhaskell Setup.lhs build
$ runhaskell Setup.lhs install

DrHylo derives point-free hylomorphisms from restricted Haskell syntax.

Usage: DrHylo [OPTION...]
  -o[FILE]  --output[=FILE]  output FILE
  -i[FILE]  --input[=FILE]   input FILE
  -f        --fix            use fixpoints instead of hylomorphisms
  -w        --pointwise      do not convert to point-free
  -O        --observable     generate observable hylomorphisms

The module Sample.hs defines some Haskell definitions that are compliant with the DrHylo supported syntax.
As an example, we can generate observable hylomorphisms for the functions frm Sample.hs into some file Out.hs:

$ DrHylo -iSample.hs -oOut.hs -O

The resulting file Out.hs can be normally interpreted with GHC as long as we have the Pointless Haskell library installed.

$ ghci Out.hs -fglasgow-exts -XUndecidableInstances

Since we asked for observable hylomorphisms, we can inspect the recursion tree for hylomorphisms via GHood. Just make sure that you have the GHood library installed (available on Hackage). A sample execution is:

> let four = Succ $ Succ $ Succ $ Succ Zero
> runO $ print $ fact four