[antlr-interest] about range float and stuff
Fabien Hermenier
hermenierfabien at gmail.com
Fri Nov 4 07:04:49 PDT 2011
Thanks Bart, I think I have understand your approach and indeed, it
seems beautiful and simple.
I will try your solution during the week-end.
Fabien.
Le 04/11/11 02:48, Bart Kiers a écrit :
> 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 <mailto: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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