[antlr-interest] lexing tips needed... (or, could I use predicate in lexer rule?)

[Micheal J]

Hi, Forgot to ask:
 
What should the lexer return for these values (note the spaces)?
".1"
"1 .1"
"1 ."
 
Micheal
 

-----------------------
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-----Original Message-----
From: antlr-interest-bounces at antlr.org
[mailto:antlr-interest-bounces at antlr.org] On Behalf Of Lloyd Dupont
Sent: 15 July 2007 02:02
To: antlr-interest at antlr.org
Subject: [antlr-interest] lexing tips needed... (or,could I use predicate in
lexer rule?)


For my parser I reaped of the lexer rules from the Java exemple.
Particularly you've got this lexer token:
NUM_FLOAT
 : DIGITS '.' (DIGITS)? (EXPONENT_PART)? (FLOAT_TYPE_SUFFIX)?
 | ............ other match
 ;
 
Now there is a problem with that!....
in the language I target everything is an object.
 
so:

"2."  is NUM_FLOAT["2."] 
"2.1"  is NUM_FLOAT["2.1"]
"2.ToString()" is NUM_INT["2"] DOT["."] ID["ToString"] LPAREN["("]
RPAREN[")]
 
So I was trying to disambiguate the lexer with a construct like that (trying
predicate in the lexer):
NUM_FLOAT
 : (
   ( DIGITS '.' EXPONENT_PART )=> DIGITS '.' (EXPONENT_PART)
(FLOAT_TYPE_SUFFIX)?
  | ( DIGITS '.' ID )=> DIGITS
  | DIGITS '.' (DIGITS)? (EXPONENT_PART)? (FLOAT_TYPE_SUFFIX)?
  )
  |    ..................... other match
;
 
but this doesn't seem to work,
1. it told me the NUM_INT rule is now not accessible anymore (I guess the
NUM_FLOAT rule absorbs it with my second alternative)
2. but more importantly an input such as "2.a" return "2." followed by
MismatchTokenException.
 
can I use predicate in lexer rule?
how could I disambiguate the NUM_FLOAT lexer rule?
I.e. being both able to read "2.3" (NUM_FLOAT) and "2.ToString()" (NUM_INT
DOT ID LPAREN RPAREN)?
 

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