parser-generators for RRPGs

Michael Dyck <>
Thu, 28 Jan 1993 02:02:26 GMT

          From comp.compilers

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Newsgroups: comp.compilers
From: Michael Dyck <>
Organization: Compilers Central
Date: Thu, 28 Jan 1993 02:02:26 GMT
Keywords: parse, tools, question, comment

Regular right-part grammars (RRPGs) are a kind of phrase structure grammar
akin to context-free grammars (CFGs). In each production of an RRPG, the
LHS is a single non-terminal (as in a CFG), but the RHS is a regular
expression (or finite automaton) over the symbol set (rather than simply a
sequence of symbols, as in a CFG).

There are various notations for writing RRPGs (or slight restrictions
thereof), many called "extended BNF".

For example (from Modula-2):

if-statement = "IF" condition "THEN" statements
                              { "ELSIF" condition "THEN" statements }
                              [ "ELSE" statements ]

It seems like most grammars presented for human consumption are RRPGs, but
most grammars presented for machine consumption are CFGs. What
parser-generators are available that accept some form of RRPG?

-Michael Dyck,
[I've seen occasional references to something called eyacc, which appeared
to be an EBNF version of yacc. Is it not the case that RRPGs can be
mechanically translated to CFGs, in which case a preprocessor for a normal
parser generator might make sense? -John]

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