[antlr-interest] lexing tips needed... (or, could I use predicate in lexer rule?)
Micheal J
open.zone at virgin.net
Sun Jul 15 05:11:26 PDT 2007
Hi,
I was really after these:
".1"
--> DOT NUM_INT["1"] ?
--> NUM_FLOAT[".1"] ?
".1 1"
--> DOT NUM_INT["1"] WHITESPACE NUM_INT["1"] ?
--> NUM_FLOAT[".1"] WHITESPACE NUM_INT["1"] ?
As for your examples, "1." is ambiguos at the lexing stage but the parser
has more context and the ambiguity disappears. If you followed my
suggestion, you just emit a NUM_FLOAT_DOT["1."] in the lexer and the parser
can deal with it as a float value or prefix to a memberAcess (i.e. the
"<object><.>" bit of an "<object><.><member>" operation).
float
: NUM_FLOAT // "1.e3"
| NUM_FLOAT_DOT // "1."
.... ;
memberAccessExpr
: ID DOT ID
| NUM_FLOAT_DOT ID // "1.echo", "1.e"
.... ;
Micheal
-----------------------
The best way to contact me is via the list/forum. My time is very limited.
-----Original Message-----
From: Lloyd Dupont [mailto:ld at galador.net]
Sent: 15 July 2007 12:11
To: Micheal J; antlr-interest at antlr.org
Subject: Re: [antlr-interest] lexing tips needed... (or,could I use
predicate in lexer rule?)
The problem is: the result really depends of what's after.
1. is ambiguous
1.e is ambiguous
1.e3 is a float
1.echo is INT DOT ID
----- Original Message -----
From: Micheal <mailto:open.zone at virgin.net> J
To: antlr-interest at antlr.org
Sent: Sunday, July 15, 2007 11:36 AM
Subject: Re: [antlr-interest] lexing tips needed... (or,could I use
predicate in lexer rule?)
Hi, Forgot to ask:
What should the lexer return for these values (note the spaces)?
".1"
"1 .1"
"1 ."
Micheal
-----------------------
The best way to contact me is via the list/forum. My time is very limited.
-----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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