Re: parsing extended CFGs, was Compiler books for beginners?

Ralph Boland asked:
> 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?


There are two answers.


1) It is simple to rewrite a grammar into the non-extended form, and
      that turns every regular expression operator into a non-terminal
      which has some advantages in terms of the type of tree constructed
      also.


2) If your parser generator accept regular expressions without
      conversion, it has to know how to reduce arbitrary length rules.
      The original parser generators did that by "lookback", but that is
      a horrible method.


Personally, we prefer that the parser generator handle the regular
expressions without conversion, and so Yacc++ does it that way.


Hope this helps,
-Chris


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Chris Clark Internet : compres@world.std.com
Compiler Resources, Inc. Web Site : http://world.std.com/~compres
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