A tool for deriving hylomorphisms http://haskell.di.uminho.pt/wiki/DrHylo

Latest on Hackage:0.0.2

This package is not currently in any snapshots. If you're interested in using it, we recommend adding it to Stackage Nightly. Doing so will make builds more reliable, and allow stackage.org to host generated Haddocks.

BSD3 licensed by Alcino Cunha, Hugo Pacheco
Maintained by Hugo Pacheco

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

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