[Haskell-cafe] generate Haskell code from model

[Brian Smith]

On 4/13/07, Steffen Mazanek <haskell at steffen-mazanek.de> wrote:
>
> Hello everybody,
>
> I would like to start a discussion on how to generate
> best-practice Haskell code from a model, e.g. from
> EMF.



I started learning Haskell precisely to solve problems like this. But, once
I got into it, I realized that Haskell is a much better modeling language
than the modeling language I was using (MOF/UML, the predecessors to EMF).
Furthermore, all the infrastructure built on top of that modeling language
was very easy to replace with Haskell code. As a result, I gave up that
effort.

You said "The benefits of the model+generate approach are well known,"
however I disagree. W3C DOM, MOF, UML, CORBA, and NetBeans 3.x-4.x are all
obvious examples of the failure of the model+generate approach. If the
modeling language is sufficiently powerful, then it should be feasible to
execute the models directly using a (custom-built) interpreter. If the
modeling language is weak then it is better to just do the modeling in
Haskell or another more powerful language.

The MDA idea was that you would have one model and then be able to use that
model in a variety of different programming languages, without having to
rewrite code in each target language. Now, people are getting this benefit
via a "code, then translate" approach. For example, GWT allows the developer
to write Java code, then generate the equivalent Javascript, without any
hand-wavy models in between. JRuby lets one write code in Ruby to be used by
code in Java; IronPython does the same for other .NET languages. In fact, C#
is basically the .NET counterpart to EMF.

FWIW, I also think that data based languages like ERD, Relax NG, and
XQuery/XPath/XML Schema are a much closer fit to Haskell than EMF. EMF is
designed to be translated any object-oriented, class-based, (soley)
subtype-polymorphic, single-dispatched, single-inheritance language; i.e.
Java. In fact, EMF is really a Java-optimized subset of what was supposed to
become part of MOF 2.0.

- Brian
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