[antlr-interest] Re: ANTLR 3.0 status: got nongreedy loops going

[thrutchy]

A few things about greediness:

- how about supporting regex-like "?" modifier (greedy=false):

CMT : "/*" ( . )*? "*/" ;

- in antlr 2.7.4 warnings and docs, it says greediness doesn't make
sense with the optional ()? construct, but it does (regex's use ??). 
greedy=true would be the same as warnWhenFollowAbiguous=false, and
non-greedy would be the same as not matching the optional construct if
it matches what's next.

- also, the java regex "+" greedy=true modifier would be nice:

"if" LPAREN expr RPAREN stat ( "else" stat )?+

I find the majority of times I use options it can be boiled down to
greediness, so the regex shorthands would be nice.

Eric


--- In antlr-interest at yahoogroups.com, Terence Parr <parrt at c...> wrote:
> Howdy,
> 
> Spent 3 days thinking this week and one hour coding to get nongreedy 
> loops going properly.  ANTLR lexers are much easier to specify now.  
> For example, here is a sample grammar I'm working with:
> 
> lexer grammar L;
> 
> IF : "if" ;
> ID : ('a'..'z')+ ;
> WS : (' '|'\n')+ ;
> CMT : "/*" ( greedy=false : . )* "*/" ;
> 
> It properly deals with IF vs ID and it handles the CMT rule properly.  
> It stops when reading when it sees "*/".  Here is the test example:
> 
> java TestLexer "bbd if /* * / ** foo */ abc"
> 
> [bbd/65538,0:0]
> [ /65539,0:0]
> [if/65536,0:0]
> [ /65539,0:0]
> [/* * / ** foo *//65540,0:0]
> [ /65539,0:0]
> [abc/65538,0:0]
> 
> TestLexer is just a loop that prints out Token objects.
> 
>          IntegerStream charStream = new ANTLRStringStream(args[0]);
>          L lexer = new L(charStream);
>          Token t = lexer.nextToken();
>          while ( t.getType()!= IntegerStream.EOF ) {
>                  System.out.println(t.toString());
>                  t = lexer.nextToken();
>          }
> 
> I feel confident that soon I'll be able to handle the Java grammar. :)
> 
> BTW, org.antlr.runtime.* is only 370 lines of code so far. :)
> 
> runtime/ANTLRStringStream.java
> runtime/CommonToken.java
> runtime/CommonTokenStream.java
> runtime/DFA.java
> runtime/IntegerStream.java
> runtime/Lexer.java
> runtime/Parser.java
> runtime/Token.java
> runtime/TokenSource.java
> runtime/TokenStream.java
> 
> L8R,
> Ter
> --
> CS Professor & Grad Director, University of San Francisco
> Creator, ANTLR Parser Generator, http://www.antlr.org
> Cofounder, http://www.jguru.com
> Cofounder, http://www.knowspam.net enjoy email again!
> Cofounder, http://www.peerscope.com pure link sharing



 
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