[antlr-interest] Lexer for floating point numbers + field access syntax with '.'
Scott Oakes
scott.oakes63 at googlemail.com
Fri Jan 29 10:30:09 PST 2010
Thanks Jim, the link looks very useful, albeit a bit daunting. I tried
amending my FLOAT to:
FLOAT
: ('0'..'9')+ ({input.LA(2) >= '0' && input.LA(2) <= '9'}?=>'.')
('0'..'9')+ EXPONENT?
| '.' ('0'..'9')+ EXPONENT?
| ('0'..'9')+ EXPONENT
;
Unfortunately I get a "rule FLOAT failed predicate" error.
On Fri, Jan 29, 2010 at 6:02 PM, Jim Idle <jimi at temporal-wave.com> wrote:
> Please see the FAQ and complete grammar at:
>
>
> http://antlr.org/wiki/display/ANTLR3/Lexer+grammar+for+floating+point%2C+dot%2C+range%2C+time+specs
>
>
> All you need do is add to the predicate here:
>
> | // We can of course have 0.nnnnn
> //
> { input.LA(2) != '.'}?=> '.'
>
> To check :
>
> { input.LA(2) != '.' && input.LA(2) >= '0' && input.LA(2) <= '0' }?=> '.'
>
> Then remove the empty alt there that allows number forms like 8.
>
> Jim
>
> > -----Original Message-----
> > From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-
> > bounces at antlr.org] On Behalf Of Scott Oakes
> > Sent: Friday, January 29, 2010 9:43 AM
> > To: antlr-interest at antlr.org
> > Subject: [antlr-interest] Lexer for floating point numbers + field
> > access syntax with '.'
> >
> > Hi, hoping for some help trying to write a lexer that allows you to
> > recognise floating point literals (2.3) as well as field accesses of
> > the
> > form x.y; see grammar below. The trouble is that an input like
> >
> > 3.fieldAccess
> >
> > Produces two tokens, FLOAT and ID, rather than the desired three, INT,
> > DOT
> > and ID.
> >
> > Pointers would be much appreciated!
> >
> > -------------------
> >
> > grammar test;
> >
> > top: expr EOF;
> >
> > expr: (INT | FLOAT | ID | '(' expr ')') (DOT ID)*;
> >
> > ID : ('a'..'z'|'A'..'Z'|'_') ('a'..'z'|'A'..'Z'|'0'..'9'|'_')*
> > ;
> >
> > INT : '0'..'9'+
> > ;
> >
> > DOT: '.';
> >
> > FLOAT
> > : ('0'..'9')+ '.' ('0'..'9')* EXPONENT?
> > | '.' ('0'..'9')+ EXPONENT?
> > | ('0'..'9')+ EXPONENT
> > ;
> >
> > WS : ( ' '
> > | '\t'
> > | '\r'
> > | '\n'
> > ) {$channel=HIDDEN;}
> > ;
> >
> > fragment
> > EXPONENT : ('e'|'E') ('+'|'-')? ('0'..'9')+ ;
>
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