Re: Implementation Language Choice

Lauri Alanko wrote:
> Gabriel Dos Reis <gdr@integrable-solutions.net> virkkoi:
>
>>Joachim Durchholz <joachim.durchholz@web.de> writes:
>
> [On pattern matching]
>
>>| Though it's beyond me why this never made it into mainstream imperative
>>| languages; it's exceedingly useful.
>>
>>Probably because people have been using the more general Visitor Pattern?
>
> The more excruciatingly painful, you mean?
>
> I once participated in writing a toy OQL compiler. The implementation
> language was preordained to be C++. We did things by the book and used
> the visitor pattern instead of "ugly" dynamic casts to discriminate
> between different syntactic classes.
>
> It was horrible, really. Having to write a trivial visit-method in
> every class, and having to write all the auxiliary visitor classes
> whenever the syntax tree had to be traversed. I couldn't help thinking
> all the time how much simpler everything would have been had we just
> used Haskell, defined a simple datatype for the abstract syntax, and
> pattern matched on the terms.


Hi,


I think in these cases the best thing would be to have double dispatch
in the language, for this reason I implemented doublecpp.


Doublecpp is a preprocessor for C++ that handles a new linguistic
construct for defining branches of a multi-method. The "right" branch
of such a method will be selected dynamically at run-time according to
the actual type of the object on which the method is invoked and to the
actual type of the first argument: double dispatch.


http://www.lorenzobettini.it/software/doublecpp/index.html


Doublecpp is free software; you are free to use, share and modify it
under the terms of the GNU General Public License (see COPYING).


hope this helps


Lorenzo
--
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| Lorenzo Bettini ICQ# lbetto, 16080134 |
| PhD in Computer Science |
| Dip. Sistemi e Informatica, Univ. di Firenze |
| Tel +39 055 4796741, Fax +39 055 4796730 |
| Florence - Italy (GNU/Linux User # 158233) |

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