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Re: Generating loops

From: Raphael 'kena' Poss
Subject: Re: Generating loops
Date: Tue, 21 Sep 2010 13:03:26 +0200

Hi Gary,

Op 21 sep 2010, om 12:53 heeft Gary het volgende geschreven:

> I should say, I'm not married to this syntax. If something else is
> easier to process then as long as it is readable as a "for" construct
> I'm not fussed.

It looks like you are tempted to use M4 to implement a compiler of sorts. While 
M4 is theoretically powerful enough to do so, experience has shown me that it 
hurts in the long run. Actually I am involved a project which more-or-less does 
what you are doing (the syntax to solve your problem could be "for(i, 1, 12)" 
instead of "for i = 1 to 12" like in C), but: after you have solved your syntax 
issue your development will become painful for two reasons:

1) as your substitution rules become more and more complex (you *will* want to 
add more and more features to your toy language), they will become gradually 
less maintainable

2) there are transformations that are non-trivial to perform with M4; say for 
example you want to define a syntax like:

    PREFIX(f, g, h) code... SUFFIX

and you want this to expand to:

    f(code...)  g(code...)  h(code...)

or anything of the kind where the same piece of input code is processed 
multiple times in different ways, your M4 code will quickly become unreadable.

Why not slapping a proper parser in your favorite functional language (Python, 
Haskell, whatever) and then celebrate the joys of high-level program 
transformation? You can ping me offline if you want some pointers about this.

Raphael 'kena' Poss · address@hidden · +31 20 525 8707
UvA · FNWI · IvI · CSA · 1098XH 904 Amsterdam (NL)

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