Re: TWIG any info (David Chase)
21 May 1996 16:18:19 -0400

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From: (David Chase)
Newsgroups: comp.compilers
Date: 21 May 1996 16:18:19 -0400
Organization: CenterLine Software
References: 96-05-094
Keywords: tools, comment () writes:
> wrt:
> TWIG code generator generator using tree pattern matching/rewriting.

> Can anybody give links to TWIG ? Where is it available
> source/binary form / at what terms/conditions for non-commercial use.

You'd probably be better off with either burg, or iburg. Iburg is most like
twig, algorithmically speaking. Burg generates faster matchers, but you
don't have as much freedom in figuring out the costs at runtime (as in, none
-- costs for patterns must be statically assigned). I think the consensus
of the people who build and use these things is that iburg's algorithm is
the one most people should use, except for applications in which speed of
code generation is extraordinarily important. (Note that I am explicitly
un-tooting my own horn here; years ago I made a decent contribution to the
technology used in burg, but I think you'd be better off with iburg. In my
own work, I would always use iburg first, and only consider burg after I had
measured the time spent generating code and found it too costly.)

My copy of iburg says:

    iburg is available for anonymous ftp from
    ( in pub/iburg.tar.Z or pub/

Here's the iburg copyright:

Copyright (C) 1993 David R. Hanson
All Rights Reserved.

Iburg is protected by copyright. It is not public-domain software,
shareware, and it is not protected by a ``copyleft'' agreement, like
the code from the Free Software Foundation.

Iburg is available free for your personal research and instructional
use under the ``fair use'' provisions of the copyright law.

You may not sell iburg or any product derived from it in which iburg is
a significant part of the value of the product. You may use the output
from iburg in products as long as you charge for only those components
that are entirely your own and you acknowledge the use of iburg clearly
in all product documentation and distribution media. You must also
request that bug reports on your product be reported to you.

My understanding of this copyright is that if you want to use iburg
to build the code generator for a compiler ("the output from iburg")
you wish to sell, provided that you comply with some simple and
non-onerous rules ("as long as ...."). I also suspect that the author
of iburg is a reasonable person, who'd be willing to explain his
intentions here in more detail if you had specific questions.

David Chase
[Dave Hanson is indeed an entirely reasonable guy, I knew him when he was at
Yale years ago. -John]

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