>I am not sure why you would call this is a semantic restriction.
Some syntactic restrictions would result in an overly complex grammar
(and parser) if specified in the grammar. Such a grammar would be too
hard to read and implement. It is more practical to use a simpler
grammar, and express the restriction as a side rule. In the same way,
it is easier to implement the parser to parse the simpler grammar and
do a separate check for the restriction after parsing.
This same approach is used for semantic restrictions that cannot be
expressed in the grammar at all. For that reason, it is common to say
that we are using a semantic restriction rather than a syntactic
restriction. It is easier to say than "a syntactic restriction that
is specified and enforced by a separate check like a semantic restriction,
rather than in the grammar."
Steven Sharp
sharp@cadence.com
Received on Wed Jun 30 14:51:17 2004
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