[antlr-interest] about range float and stuff
Bart Kiers
bkiers at gmail.com
Fri Nov 4 01:48:00 PDT 2011
Hi Fabien,
Handling this in the parser will make your life much harder than it has to.
Doing it in the lexer, you will need a bit of custom code, but I'd go for
something similar to this (something like it is on the WIki somewhere, but
can't find it...):
grammar RangeDemo;
@lexer::members {
java.util.Queue<Token> tokens = new java.util.LinkedList<Token>();
public void offer(int ttype, String ttext) {
emit(new CommonToken(ttype, ttext));
}
@Override
public void emit(Token t) {
state.token = t;
tokens.offer(t);
}
@Override
public Token nextToken() {
super.nextToken();
return tokens.isEmpty() ? Token.EOF_TOKEN : tokens.poll();
}
}
parse
: (t=. {System.out.printf("\%-10s \%s\n", tokenNames[$t.type],
$t.text);})* EOF
;
FLOAT
: INT '..' {offer(INT, $INT.text); offer(RANGE, "..");}
| OCTAL '..' {offer(OCTAL, $OCTAL.text); offer(RANGE, "..");}
| '.' DIGITS
| DIGITS '.' DIGITS?
;
RANGE
: '..'
;
INT
: '1'..'9' DIGIT*
| '0'
;
OCTAL
: '0' ('0'..'7')+
;
fragment DIGITS : DIGIT+;
fragment DIGIT : '0'..'9';
SPACE
: (' ' | '\t' | '\r' | '\n') {skip();}
;
And if you run the class:
import org.antlr.runtime.*;
public class Main {
public static void main(String[] args) throws Exception {
String src = "..07..8.5 1.9..02 1..3.4";
RangeDemoLexer lexer = new RangeDemoLexer(new ANTLRStringStream(src));
RangeDemoParser parser = new RangeDemoParser(new
CommonTokenStream(lexer));
System.out.println("Parsing: '" + src + "'");
parser.parse();
}
}
You'll see the following being printed to the console:
Parsing: '..07..8.5 1.9..02 1..3.4'
RANGE ..
OCTAL 07
RANGE ..
FLOAT 8.5
FLOAT 1.9
RANGE ..
OCTAL 02
INT 1
RANGE ..
FLOAT 3.4
Regards,
Bart.
On Fri, Nov 4, 2011 at 7:28 AM, Fabien Hermenier
<hermenierfabien at gmail.com>wrote:
> Hi
>
> In an earlier version of my language, I had to parse range of integers
> in various base. Now I want to include float. I have read
>
> http://www.antlr.org/wiki/display/ANTLR3/Lexer+grammar+for+floating+point,+dot,+range,+time+specs
> but I've still got some questions.
>
> All the work seems to be done at the lexer level so the type of the
> following tokens will be as example:
> 5 : DECIMAL_LITTERAL
> 07 : OCTAL_LITTERAL
> 7.5: FLOATING_POINT_LITTERAL
> 5..7 : DOTDOT
>
> In the last example, the result is not very convenient because I will
> still have to extract the bounds
> and compute their type by myself which seems quite redundant with the
> job performed by the lexer.
> May be I am missing something ?
>
> I would rather be able to express the range at the parser level which
> seems much more convenient to me:
> range: FLOATING_POINT_LITTERAL DOTDOT FLOATING_POINT_LITTERAL.
> In this way, I will also be able to manage the possible spaces between
> the bounds and the DOTDOT.
>
> So, am I right to try to parse range at the parser level ? Or is there a
> solution to extract easily the bounds with their type if I am doing the
> job at the lexer level ?
>
> Thanks in advance,
> Fabien.
>
>
>
>
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