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philosophy.txt
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philosophy.txt
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=begin copyright
reg - the ruby extended grammar
Copyright (C) 2016 Caleb Clausen
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
=end
That's a long story, and well worth telling.
A long time ago, I wanted a better regexp than regexp. My search ended
when I found an extremely obscure language called gema (the
general-purpose matcher). I'm guessing that I'm the only person to ever
take gema seriously. For a time, I became the worlds foremost expert on
gema. Gema is designed around the idea that all computation can be
modeled as pattern and replacement. Everything in gema is pattern and
replacement... essentially everything is done with regexps. I was
fascinated with the idea. This seemed to me to be a much better model
for most programming problems, which typically involve reading input,
tranforming it in some way, and writing it out again. Conventional
languages (starting with fortran, and including ruby) are based around
the idea of a program being a long string of formulas. This is great
for math-heavy stuff, but most programming is really about data
manipulation, not math.
But there was trouble in paradise. Gema was wonderful, but weird. The
syntax was cranky. The author had issued one version long ago then
disappeared. Gema code was hard to read, in part because
everythingwasalljammedtogether .
Ifyouinsertspacestomakeitmorer eadable,itchangesthesemanticso fyourprogram.
There were strange problems that I never tracked down or fully
characterized. The only data-type was the string. You had to be an
expert at avoiding the invisible pitfalls of the language to get
anywhere. But I did get surprisingly far. I managed to coax gema into
becoming a true parser, and parsing a toy language.
I wanted to write a compiler in gema. Yes, the whole compiler. And
parsing the toy language was already straining its capabilites. It
wasn't the data model; I actually figured out how to model all other
data types using strings. A match-and-replace language is actually much
better suited to most compiler tasks than an algol-like formula
language.
Eventually, I abandoned gema, determined to recreate it's glory in a
cleaner form. It was at about this time that I discovered ruby. The
successor to gema was ruma, the ruby matcher. Ruma would be basically
just like gema, but without the problems. Whitespace allowed between
tokens. Proper quotation mechanisms, including nested quotes. And the
language used in the actions (replacements) would be full ruby, instead
of gema's inadequate and crude action language.
Ruma got maybe halfway done... quite a ways, really. As part of ruma, I
needed a ruby lexer to make sense of the actions. This turned out to be
quite a lot harder than I had anticipated; I'm still working on that
lexer.
After grinding away at the lexer for a while, dreaming of ruma in the
meantime, I had a brainstorm. Ruma, like gema, was to be a string-based
language. It only operated on strings. In gema, that was just fine
because everything was strings and you just had to live with that. But
ruby has all these other types, a real type system. Wouldn't it be nice
to have those sophisticated search capabilites for other types too?
Well, since I proved to myself that all data types can be converted to
strings, why not convert the ruby data into strings and then match that
in ruma. Of course, it would be so much nicer to just do the matching
on the data in it's original form....
The breakthrough came when I realized how malleable ruby really is. I
had become accustomed to c, which I still love, but in so many ways
it's so much more limited. I didn't really have to write my own parser
and lexer; ruby could do it all for me. I just had to override a bunch
of operators.
After that, it was simple. All I do is override the right operators,
and ruby does the parsing and hands me the match expressions in
already-parsed form. Reg is amazingly small in the end. Most of the
effort and code went into the array matcher, but at least as much
functionality is to be had from the hash and object matchers, which
were trivial.