🚀 go-pugleaf

Posting-Front-End: GNU Emacs 18.47.9 of Mon Mar 21 1988 on ruuinf (hcx/ux)


In article <11532@shemp.CS.UCLA.EDU> gast@lanai.cs.ucla.edu (David Gast) writes:
   2) There are other grammar formalisms besides CFGs.  For example, vW
      or two level grammars.  While the typical reader may not want to
      read a vW grammar, the language could be defined with a vW grammar
      so that compiler writers could check their compilers.  The user
      could be told about indentation.

      It might also be possible, to use the Grammar Rule Notation, a la
      Prolog to describe the indentation levels.  I do not know (because
      I have not really considered it). The GNR is more powerful than
      a CFG.  An extra argument to the grammar rules could indicate the
      level of indentation.

Currently I think Attribute Grammars (AG) are the most useful things in
grammar land. They are a little bit less powerful than vW grammars, but
rightly so, as vW grammars are generally not decidable (i.e. it is not
generally possible to automatically make a compiler from a vW grammar; for
some grammars there isn't even a parser possible). An AG takes just that
extra structure that makes it much more useful. It is very easy to write an
AG that takes declaration before use into account.

I haven't compared GNR with AG, so I don't know how they compare, but they
look a bit similar.

-- 
Piet van Oostrum, Dept of Computer Science, University of Utrecht
Budapestlaan 6, P.O. Box 80.012, 3508 TA Utrecht, The Netherlands
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Telephone: +31-30-531806              UUCP: ...!mcvax!ruuinf!piet