The DrHylo package

[Tags:bsd3, library, program]

DrHylo is a tool for deriving hylomorphisms from a restricted Haskell syntax. It is based on the algorithm first presented in the paper Deriving Structural Hylomorphisms From Recursive Definitions at ICFP'96 by Hu, Iwasaki, and Takeichi. The generated code can be run with Pointless Haskell (, allowing the visualization of the recursion trees of Haskell functions.

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Versions 0.0.1, 0.0.2
Dependencies array (>=0.1), base (>=4), containers, haskell-src-exts (==, mtl, pointless-haskell, pretty (>=1.0), syb [details]
License BSD3
Author Alcino Cunha <>, Hugo Pacheco <>
Maintainer Hugo Pacheco <>
Category Language
Home page
Uploaded Tue Dec 9 10:37:32 UTC 2008 by HugoPacheco
Distributions NixOS:0.0.2
Downloads 722 total (10 in the last 30 days)
0 []
Status Docs not available [build log]
All reported builds failed as of 2016-10-25 [all 15 reports]
Hackage Matrix CI


  • Language
    • Pointfree
      • Language.Pointfree.Parser
      • Language.Pointfree.Pretty
      • Language.Pointfree.Syntax
    • Pointwise
      • Language.Pointwise.Matching
      • Language.Pointwise.Parser
      • Language.Pointwise.Pretty
      • Language.Pointwise.Syntax


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Maintainer's Corner

For package maintainers and hackage trustees

Readme for DrHylo

Readme for DrHylo-0.0.2


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