Decl

Depending how you look at it, Decl is either a programming language or a really
complicated framework for Perl that allows complex data structures to be declared
instead of being built step-by-step in an initialization phase.

I first started using it in the context of WxPerl, a GUI library for Perl; construction
of the user interface for a Wx program can be a lengthy process.  My idea was
simply to write a pseudocode interpreter that could do it for me.  The definition
of an entire GUI program for temperature conversion (80 lines of Perl in the
old WxPerl distribution) thus reduces to this:

  dialog (xsize=250, ysize=110) "Wx::Declarative dialog sample"
    field celsius (size=100, x=20, y=20) "0"
    button celsius (x=130, y=20) "Celsius" {
        $^fahrenheit = ($^celsius / 100.0) * 180 + 32; 
    }
    field fahrenheit (size=100, x=20, y=50) "32"
    button fahrenheit (x=130, y=50) "Fahrenheit" {
        $^celsius = (($^fahrenheit - 32) / 180.0) * 100;
    }

Decl has significant indentation, with all the problems that entails for large
nested structure, but the idea is to keep things concise.  There are two ameliorating
influences: first, there is a mechanism to flatten complex structure to permit saner
presentation, and second, embedded code (e.g. Perl) is not significantly indented,
and I expect most of the heavy lifting to happen there anyway.

In addition to declaration of complex structure, Decl also provides a macro system
that can target any language (my current obsession).  I'm in the process of
building a Web publishing system on top of the macro engine.

LICENSE AND COPYRIGHT

Copyright (C) 2010-2011 Michael Roberts

This program is free software; you can redistribute it and/or modify it
under the terms of either: the GNU General Public License as published
by the Free Software Foundation; or the Artistic License.

See http://dev.perl.org/licenses/ for more information.


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