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Postings from May 2003
On Wed, May 14, 2003 at 10:47:06PM -0000, Ilya Zakharevich wrote:
> On Wed, May 14, 2003 at 03:07:05PM -0700, Edward Peschko wrote:
>
> Sorry, I could not guess what you have in mind...
>
> Yours,
Suppose you had the following code:
my $string = 'abcdefg';
sub _position_increment
{
my ($string,$pos) = @_;
return($pos+3);
}
my $_coderef = \&_position_increment;
if ($string =~ m"($_coderef)")
{
print $1; # prints 'abc';
}
I'd want - the moment the regular expression sees $_coderef, for perl to run the function
underlying coderef, passing it the string and the position at which the string was at
when coderef was run.
So - stepping through:
my $string = 'abcdefg'; # pos($string) == 0;
sub _position_increment
{
my ($string, $pos) = @_; # when we see this function, increment pos by 3
return($pos+3); # return the new position because we are
} # automatically succesful. (if we wanted a non
# successful match, return(-1);
my $_coderef = \&_position_increment;
if ($string =~ m"($_coderef)")
{
print STDERR "$1"; # the engine knows we went in with a pos of 0
# and came out with a pos of 3, hence it saves
# 'abc' in backreference
}
There's a hook into @INC to do a similar thing:
push(@INC, \&function_modifying_inc_at_point_of_use);
which runs a coderef each time an '@INC' is seen.
Anyways, the point is that the proposed syntax is a lot more intuitive than (?...) since
the syntax is cleaner, its backwards compatible with the current regex engine, and it
integrates better with C code. Ultimately, I'd like to be able to write:
int _parens( char *str, int pos)
{
int len = strlen(str);
while (str[pos++] != '(' && pos < len) { }
while (str[pos++] != ')' && pos < len) { }
if (pos == len) return(-1)
return(pos);
}
my $_parens = \&_parens;
if ($string =~ m"($_parens)stuff")
{
}
and have the regular expression engine:
a) recognize that $_parens is a code reference
b) run the code behind that coderef
c) increment pos to the position where the first ')' is seen. (as per c code)
d) auto-fail (with a -1) if no ')' is seen
e) continue on to match the string 'stuff' after the pos returned by the function
_parens.
In other words, I want the ability to put my own C hooks inside the regex engine.
Ed
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