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From: pgl@cup.portal.com
Newsgroups: comp.compilers
Subject: Re: Compiler with adjustable parsers
Keywords: prolog
Message-ID: <1990Mar3.062743.26438@esegue.segue.boston.ma.us>
Date: 3 Mar 90 06:27:43 GMT
Sender: compilers-sender@esegue.segue.boston.ma.us
Reply-To: pgl@cup.portal.com
Organization: Compilers Central
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Approved: compilers@esegue.segue.boston.ma.us

> Does anyone know of a compiler/language that allows you to specify changes
> to how the language is parsed (in part at least) from withing the program.

Sure: Prolog allows (re)defining operators.  In addition, IBM-Prolog
allows specifying various other syntax items, by changing its scan
tables and its table of "assignable atoms".  For example, it allows
the Edinburgh syntax:
	a([X|_y],_) :- b(X), !, c(X,_y) .
and, by simply changing these tables and defining different operators,
the default IBM syntax, modified for keyboards without square brackets:
	a({X!*y},*) <- b(X) & / & c(X,*y) .

What's more, you can input a clause in one syntax, change the syntax and
then get the clause back in the new syntax (using clause/2 or ax(*,*)).

The parser is quite fast because during processing, all atoms must
be hashed anyway, so comparing against an "assignable atom" is just
a pointer comparison.

- peter ludemann	pgl@cup.portal.com	[standard disclaimer]
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