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From: debray@sbcs.UUCP
Newsgroups: net.lang
Subject: Re: Lexical analyzers and parsers
Message-ID: <628@sbcs.UUCP>
Date: Mon, 14-May-84 17:35:42 EDT
Article-I.D.: sbcs.628
Posted: Mon May 14 17:35:42 1984
Date-Received: Thu, 17-May-84 05:31:57 EDT
References: <174@ccieng2.UUCP>
Organization: SUNY at Stony Brook
Lines: 34

<!>
	> Any language that you have to parse most of a line and then back
	> up to find the token (like fortran) has severe brain damage.
	> Consider:
	>
	> IF(I.EQ.2)22,23,22
	>
	> It isn't until we hit the first comma that fortran realizes it is
	> not looking at an identifier! It then realizes that an identifier
	> cannot be followed by a comma, and backs up looking for a reserved
	> word!!!!!!

(1) I agree that FORTRAN isn't a dream language.  It's been years since I've
touched the language, but if memory serves me right, FORTRAN identifiers
can't have special symbols like '(' and '.' in them, so I'm not sure how
valid the above example is.  The DO statement, 

	DO 100 J = 1, 10

might be the example you're looking for.

(2) In general, backing up in execution is a pretty messy affair, and to my
knowledge, only one language, Prolog, does a decent job of it. The problem,
of course, is with undoing global changes, e.g. to the symbol table. In the
above example, though, it would seem that simply increasing the amount of
lookahead would take care of the problem.
-- 
Saumya Debray, 	SUNY at Stony Brook

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