https://bugs.exim.org/show_bug.cgi?id=2301
Mehmet gelisin <mehmetgelisin@???> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |mehmetgelisin@???
--- Comment #6 from Mehmet gelisin <mehmetgelisin@???> ---
Essentially: Remove this restriction from PCRE
Recursion processing in PCRE differs from Perl in two important ways.
In PCRE (like Python, but unlike Perl), a recursive subpattern call is
always treated as an atomic group. That is, once it has matched some of
the subject string, it is never re-entered, even if it contains untried
alternatives and there is a subsequent matching failure.
http://www.compilatori.com/
It leads to unparseable context-sensitive grammars like:
{ S -> 0B1 | 1B0 | 1C1 | 0C0,
A -> 0 | 1,
B -> ABA | D1,
C -> ACA | D0,
D -> _E | _ ,
E -> AE | A }
This is essentially adding two bits at a same offset of two binary numbers and
checking if it matches the trailing bit. [The actual goal was matching correct
additions of two binary numbers in form of a + b = c where a, b and c each
match [01]+.]
http://www.wearelondonmade.com/
I wished this could be expressed as:
(?(DEFINE)
(?<s> 0(?&b)1 | 1(?&b)0 | 1(?&c)1 | 0(?&c)0 )
(?<a> 0 | 1 )
(?<b> (?&a)(?&b)(?&a) | (?&d)1 )
(?<c> (?&a)(?&c)(?&a) | (?&d)0 )
(?<d> _(?&e) | _ )
(?<e> (?&a)(?&e) | (?&a) )
)
http://www.jopspeech.com/
^(?&s)$
Example matches:
0_00
01_101
Example non-matches:
0_01
100_00011
http://joerg.li/
In case this is declined, _why_ is PCRE exhibiting that behavior?
Essentially: Remove this restriction from PCRE
http://connstr.net/
Recursion processing in PCRE differs from Perl in two important ways.
In PCRE (like Python, but unlike Perl), a recursive subpattern call is
always treated as an atomic group. http://embermanchester.uk/ That is,
once it has matched some of
the subject string, it is never re-entered, even if it contains untried
alternatives and there is a subsequent matching failure.
http://www.slipstone.co.uk/
It leads to unparseable context-sensitive grammars like:
{ S -> 0B1 | 1B0 | 1C1 | 0C0,
A -> 0 | 1,
B -> ABA | D1,
C -> ACA | D0,
D -> _E | _ ,
http://www.logoarts.co.uk/
E -> AE | A }
This is essentially adding two bits at a same offset of two binary numbers and
checking if it matches the trailing bit.
http://www.acpirateradio.co.uk/ [The
actual goal was matching correct additions of two binary numbers in form of a +
b = c where a, b and c each match [01]+.]
I wished this could be expressed as:
(?(DEFINE)
https://waytowhatsnext.com/
(?<s> 0(?&b)1 | 1(?&b)0 | 1(?&c)1 | 0(?&c)0 )
(?<a> 0 | 1 )
(?<b> (?&a)(?&b)(?&a) | (?&d)1 )
(?<c> (?&a)(?&c)(?&a) | (?&d)0 )
(?<d> _(?&e) | _ )
https://www.webb-dev.co.uk/
(?<e> (?&a)(?&e) | (?&a) )
)
^(?&s)$
Example matches:
0_00
http://www.iu-bloomington.com/
01_101
Example non-matches:
0_01
100_00011
http://www-look-4.com/
In case this is declined, _why_ is PCRE exhibiting that behavior?
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