The signs of literals

Hung-Ta Lin <lin@cs.monash.edu.au>
7 Dec 1997 22:07:12 -0500

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The signs of literals lin@cs.monash.edu.au (Hung-Ta Lin) (1997-12-07)
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From: Hung-Ta Lin <lin@cs.monash.edu.au>
Newsgroups: comp.compilers
Date: 7 Dec 1997 22:07:12 -0500
Organization: Compilers Central
Keywords: syntax, design

Hi, I am working on a grammar that explicitly treats sign as part of a
integer literal:


...
exp5 ::= [+|-] exp6
exp6 ::= integer_literal | ...


integer_literal::= [+|-] digit {digit}


The grammar is ambiguous because:


FIRST([+|-] exp6) == FOLLOW([+|-] exp6) = { PlusToken, MinusToken }.


That is, given a + or -, it is not clear whether it is the beginning of a
exp5 or integer_literal.


Would it be okay to change that grammar to:


exp5 ::= [+|-] exp6
exp6 ::= integer_literal | ...


integer_literal ::= digit {digit}


or I should treat integer_literal as a lexical token:


(+|-)?[0-9]+
?


The former disallows expressions such as + - 4; the latter requires no
space between the sign and the digit sequence.


Any comment is welcome.


Thanks,
Lin
--
Lin Hung-Ta email: lin@cs.monash.edu.au
Department of Computer Science Monash Univeristy, Clayton, Australia
--

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