strange behavior of a grammar test in the Perl 6 shell. [see the comments. The problem is not what I originally described]The first two results are expected but not the third and the fourth that should match as well.Expected results : the b rules matches except at the second iteration. Because of the procedural alternation with the rule bdesigne…

gistfile1.txt

> for '', 'a', 'aa', 'aaa'  -> $t { say $! unless try say ( grammar { token TOP { <a> || <b> } ; token a { '[' ~ ']' a }; token b { "[$t]" } }).parse: "[$t]" }

｢[]｣
 b => ｢[]｣

｢[a]｣
 a => ｢[a]｣

Unable to parse expression in a; couldn't find final ']'
  in any FAILGOAL at src/stage2/QRegex.nqp:1037
  in method parse at src/gen/CORE.setting:10695
  in method reify at src/gen/CORE.setting:6010
  in method reify at src/gen/CORE.setting:5905
  in method gimme at src/gen/CORE.setting:6333

Unable to parse expression in a; couldn't find final ']'
  in any FAILGOAL at src/stage2/QRegex.nqp:1037
  in method parse at src/gen/CORE.setting:10695
  in method reify at src/gen/CORE.setting:6010
  in method reify at src/gen/CORE.setting:5905
  in method gimme at src/gen/CORE.setting:6333

> 

gram.p6

grammar A {  
  token TOP { <a> || <b> } ; 
  token a { '[' ~ ']' a }; 
  token b { { say $*t.perl } "[$*t]"  }
};
for '', 'a', 'aa', 'aaa' {
 say "+$_";
 try {
   say "-$_";
   my $*t = "[$_]";
   $/ = A.parse: $*t;
   say $/.perl;
 }
}

I think the first result must be rejected if 'the ~ construct adds a "fail the match" component'

Indeed I missed the pmichaud comment about "fail the match" for the ~ construct when it fails. I can't give the link beause irc log is down.

I don't see anything about "fail the whole match" for the tilda operator in S05

the ~ construct adds a "fail the match" component source: http://colabti.org/irclogger/irclogger_log/perl6?date=2013-06-23#l1118