Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!markh
From: markh@csd4.milw.wisc.edu (Mark William Hopkins)
Newsgroups: comp.lang.prolog
Subject: Bootstrapping precedence grammars.
Message-ID: <3635@csd4.milw.wisc.edu>
Date: 31 Jul 89 22:44:13 GMT
Sender: news@csd4.milw.wisc.edu
Reply-To: markh@csd4.milw.wisc.edu (Mark William Hopkins)
Organization: University of Wisconsin-Milwaukee
Lines: 20

Simple question:

   Can Prolog's read(X) predicate be defined using only the character
predicates for I/O?  In other words, does Prolog have the capacity to
bootstrap its own precedence grammar, using the operator declarations
made by the op predicate?

   I believe the answer is no, because (and ONLY because)

                         op(Prec, Type, Rator)

cannot be used in the mode

			 op(OUTPUT, OUTPUT, INPUT),

to find the precedence and fixity of an operator, but only in the mode

		         op(INPUT, INPUT, INPUT).

to set it.