Pointless Haskell

Introduction

Pointless Haskell is library for point-free programming with recursion patterns defined as hylomorphisms. It is part of the UMinho Haskell Libraries that are being developed in the Research.PURe project. The core of the library is described in the following paper.

• Personal.Alcino Cunha. Point-free Programming with Hylomorphisms. To be submitted.

It also allows the visualization of the intermediate data structure of the hylomorphisms with GHood. This feature toghether with the DrHylo tool allows us to easily visualize recursion trees of Haskell functions. We first implemented this ideas using Generic Haskell, as presented in WFLP'03. We now take a different approach to genericity based on Personal/Alcino.PolyP.

• Personal.Alcino Cunha. Automatic Visualization of Recursion Trees: a Case Study on Generic Programming. In volume 86.3 of ENTCS: Selected papers of the 12th International Workshop on Functional and (Constraint) Logic Programming. 2003.

Download

The latest snapshot of the UMinho Haskell Libraries can be downloaded here. The modules that comprise Pointless Haskell are the following.

Module	Description
Pointless.RecursionPatterns	Definition of the typical recursion as hylomorphisms.
Pointless.Observe.RecursionPatterns	Recursion patterns with observation of intermediate data structures.
Pointless.Observe.Functors	Definition of generic observations.
Pointless.Isomorphisms	Auxiliary isomorphism definitions.
Pointless.Functors	Definition of functors, generic maps, and sum-of-products representation.
Pointless.Examples.Examples	Lots of examples.
Pointless.Combinators	Point-free programming combinators.
Pointless.Combinators.Uncurried	Point-free definitions of uncurried versions of the basic combinators.
Debug.Observe	Slightly modified GHood library.

Usage

For the moment there is no documentation, but by reading the papers and looking at examples you should be able to learn it by yourself. It was only tested on GHC. I think that it should be easy to use it under Hugs.

Please send feedback to alcino@di.uminho.pt.

DrHylo

Introduction

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.

Download

See PUReSoftware.

Usage

To use DrHylo, simply type DrHylo -h at the command line, and follow instructions.

Usage: Personal/Alcino.DrHylo [OPTION...]
  -o[FILE]  --output[=FILE]  output FILE
  -i[FILE]  --input[=FILE]   input FILE

To run the resulting Haskell files you will need PointlessHaskell.

Please send feedback to alcino@di.uminho.pt.

Point-free Program Transformation

This is a project where I, José Proença, worked on since April until October 2005. It was supervised by Jorge Sousa Pinto and Alcino Cunha, who supported and helped me during this time. The proposal is explained in more detailed in here. The results can be found in my internship report, here.

The project consists on two parts:

• Definition of two refactorings -- the conversion from point-wise to pointfree and the removal of guards;
• Automatic simplification and transformation of pointfree expressions.

Refactorings in HaRe

In the begining of the project, I spent two weeks in Canterbury developing two refactorings to be part of HaRe:

• Convertion of point-wise code to pointfree;
• Removal of guards.

A snapshot of the source code where these transformations are applied can be found here.

There are also some examples that can be found in the following links:

• Examples of the translation point-wise - pointfree;
• Examples of the removal of guards.

The SimpliFree Tool

Allows for the automatic simplification and some program transformation of Haskell code, written in a point-free style. The technical report is available here. The SimpliFree tool is now available in the Uminho Haskell Libraries, that can be downloaded from the CVS repository.

This tool uses Haskell pattern matching to apply rules, by creating an auxiliary file with the functions where the strategies, rules and the pointfree terms are defined. In spite of the fact that this approach meant to be simpler than most approaches where a pattern matching algorithm is defined, the definitions of functions that apply a rule were more complex than expected.

In September, this tool, together with the DrHylo tool and the Pointless library, were presented in IFL'05 workshop. The presentation "A Framework for Point-free Program Transformation", shown in this workshop, can be found here.

The SimpliFree tool was also presented in the PURe Workshop 2005. The slides can be found here.