From ekiru.0@gmail.com

[1​:38pm] tylercurtis​: rakudo​: grammar Foo { token TOP { 'b' } }; say
Foo.parse('abc').Bool; # this is right
[1​:38pm] p6eval​: rakudo 19931f​: OUTPUT«0␤»
[1​:38pm] tylercurtis​: rakudo​: grammar Foo { token TOP { 'b' } }; say
Foo.parse('bc').Bool; # I don't think this is.
[1​:38pm] p6eval​: rakudo 19931f​: OUTPUT«1␤»
[1​:38pm] tylercurtis​: rakudo​: grammar Foo { token TOP { 'b' } }; say
Foo.parse('ab').Bool; # Also right.
[1​:38pm] p6eval​: rakudo 19931f​: OUTPUT«0␤»
[1​:39pm] tylercurtis​: Grammar.parse seems to anchor to the beginning
of the string but not to the end.

If I correctly understand the behavior of Grammar.parse and regex
methods, only "b" should match the Foo grammar above because regex
methods are automatically anchored to the beginning and end of the
string when called directly as Grammar.parse should do with Foo.TOP.

--
Tyler Curtis

From @masak

ekiru (>)​:

[1​:38pm] tylercurtis​: rakudo​: grammar Foo { token TOP { 'b' } }; say
Foo.parse('abc').Bool; # this is right
[1​:38pm] p6eval​: rakudo 19931f​: OUTPUT«0␤»
[1​:38pm] tylercurtis​: rakudo​: grammar Foo { token TOP { 'b' } }; say
Foo.parse('bc').Bool; # I don't think this is.
[1​:38pm] p6eval​: rakudo 19931f​: OUTPUT«1␤»
[1​:38pm] tylercurtis​: rakudo​: grammar Foo { token TOP { 'b' } }; say
Foo.parse('ab').Bool; # Also right.
[1​:38pm] p6eval​: rakudo 19931f​: OUTPUT«0␤»
[1​:39pm] tylercurtis​: Grammar.parse seems to anchor to the beginning
of the string but not to the end.

If I correctly understand the behavior of Grammar.parse and regex
methods, only "b" should match the Foo grammar above because regex
methods are automatically anchored to the beginning and end of the
string when called directly as Grammar.parse should do with Foo.TOP.

I went looking for support of this view in S05. Didn't find any.

The reason the 'b' is only matched at the beginning of the string in the examples above has
nothing to do with the grammar anchoring to the beginning of the string, but is a consequence
of the 'token' keyword turning backtracking off, and starting the match at a new position counts
as a form of backtracking.

Rejecting the ticket.

The RT System itself - Status changed from 'new' to 'open'

@masak - Status changed from 'open' to 'rejected'