Re: regular expression operators in CF grammars

SLK Parsers <parsersinc@yahoo.com> wrote:
> > While this question is being asked I would like to know if any
> > compiler/parser textbooks deal with grammars that use regular
> > expression operators. This is particularly relavent to LL based
> > parsing because most LL based parsing tools now support extended CFGs.
> > Why has LR based parser generator tools that directly support (that do
> > not translate the grammar into non-extended form) regular expression
> > operators so uncommon anyway; other than that they are fairly complex?
>
> The classical, and proven grammar analysis algorithms in parsing
> theory are based on definitions that do not include a notion of
> regular expressions as in EBNF. Adhoc programming methods that
> internally translate EBNF run the risk of introducing incorrectness.


I've spent the last week writing a recursive descent parser, and my
experience is a bit different from yours. For me, writing functions
that encapsulated common patterns greatly simplified the parser and
made it much more readable. All but one of those common patterns were
the regular operators: +, *, ?. (The one was bracketed, delimited
sequences, like '(x, y, z)' or '{foo; bar; baz}'.)


I found that this also made the grammar easier to understand, because
there were fewer productions in it.
--
Neel Krishnaswami
neelk@alum.mit.edu

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