[Haskell-cafe] Compositional Compiler Construction, Oberon0 examples available

Doaitse Swierstra doaitse at swierstra.net
Mon Aug 20 10:17:34 CEST 2012

On Aug 19, 2012, at 10:40 , Heinrich Apfelmus <apfelmus at quantentunnel.de> wrote:

> Doaitse Swierstra wrote:
>> Over the years we have been constructing a collection of Embedded
>> Domain Specific Languages for describing compilers which are
>> assembled from fragments which can be compiled individually. In this
>> way one can gradually ``grow a language'' in a large number of small
>> steps. The technique replaces things like macro extensions or
>> Template Haskell; it has become feasible to just extend the language
>> at hand by providing  extra modules. The nice thing is that existing
>> code does not have to be adapted, nor has to be available nor has to
>> be recompiled.
>> Recently we have been using (and adapting) the frameworks such that
>> we could create an entry in the ldta11 (http://ldta.info/tool.html)
>> tool challenge, where one has to show how one's tools can be used to
>> create a compiler for the Oberon0 language, which is used a a running
>> example in Wirth's compiler construction book.
>> We have uploaded our implementation to hackage at:
>> http://hackage.haskell.org/package/oberon0.
>> More information can be found at the wiki:
>> http://www.cs.uu.nl/wiki/bin/view/Center/CoCoCo
>> You may take a look at the various Gram modules to see how syntax is
>> being defined, and at the various Sem modules to see how we use our
>> first class attribute grammars to implement the static semantics
>> associated with the various tasks of the challenge.
>> We hope you like it, and comments are welcome,
> Awesome!
> I have a small question: Last I remember, you've mainly been using your UUAGC preprocessor to write attribute grammars in Haskell, especially for UHC. Now that you have first-class attribute grammars in Haskell ("achievement unlocked"), what do you intend to do with the preprocessor? How do these two approaches compare at the moment and where would you like to take them?
> Best regards,
> Heinrich Apfelmus

On the page http://www.cs.uu.nl/wiki/bin/view/Center/CoCoCo there is a link (http://www.fing.edu.uy/~mviera/papers/VSM12.pdf) to a paper we presented at LDTA (one of the ETAPS events) this spring. It explains how UUAGC can be used to generate first class compiler modules. 

We have also a facility for grouping attributes, so one can trade flexibility for speed. The first class approach stores list of attributes as nested cartesian products, access to which a clever compiler might be able to optimize. This however would correspond  a form of specialisation, so you can hardly say that we have really independent modules; as always global optimisation is never compositional). From the point of view of the first class approach such grouped non-termionals are seen as a single composite non-terminal. 


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