Re: gnat.spitbol.patterns.match(...)

[Robert Dewar <robert_dewar@my-deja.com>]

In article <3A04F805.AB1D83DA@telepath.com>,
  Ted Dennison <dennison@telepath.com> wrote:
> Well...a lot of that was SPITBOL (a regular expression
> language).


That's a lot of misinformation in a very short sentence :-) :-)

1. Spitbol is not a language, it is an implementation. Referring
to Spitbol as a language would be like referring to GNAT as
a language. The language is SNOBOL 4, designed by Ralph Griswold
and coworkers at Bell Labs in the late 70's and early 80's.
I also partipated in the language design. The reason that we
call the package Spitbol in GNAT is fourfold:

   1. It incorporates some of the extensions of SPITBOL
   2. Most SNOBOL-4 users these days are using SPITBOL
   3. It uses the pattern matching algorithms of SPITBOL
   4. Since I wrote SPITBOL, it creates an useful connection

2. It has NOTHING at ALL to do with regular expressions. I
really don't know where you got this idea. The whole point of
SNOBOL 4 is that its pattern matching is based on context free
grammars, and actually it is better to think of them as
attribute grammars, since quite general semantic actions,
including predicates can be included in a pattern.

Indeed the use of regular expressions for matching is by
comparison kludgy and very restrictive.

To give an idea of the power of SNOBOL-4 pattern matching, it
is quite feasible to write a pattern that matches only strings
that are syntactically valid Ada 95 programs, and rejects all
other strings. The syntax of this pattern would be reminiscent
of the BNF used in the Ada RM to describe the syntax of Ada.

Robert Dewar


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