Re: Recursive substitution

[bobf]

in reply to Recursive substitution

I like to take a very simple approach to such things, since the tricky methods usually confuse me when I come back to it 6 months later and have to modify it somehow. :-)

my $s = 'ab';
my $pat = qr/^(a{1,3})(?=b)/;

while( $s =~ m/$pat/ )
{
    $s =~ s/$pat/$1a/g;
}

Or, if you prefer more of the 1-liner feel:

my $s = 'ab';
my $pat = qr/^(a{1,3})(?=b)/;

do{ $s =~ s/$pat/$1a/g } while $s =~ m/$pat/;

I'm sure it is possible to do this in the regex itself (probably with /e). I'm sure other monks will enlighten both of us.

Update: I changed approaches mid-code and forgot to remove the superfluous m//. These solutions are not very perlish.

[JadeNB]

Thanks very much. I realised shortly after posting that I hadn't explained why I didn't want the most natural answer (current explanation: because I don't, that's why), but didn't update my post in time.

By the way, I think that s/$pat/$sub/ is (effectively) a no-op unless m/$pat/, so I think that it's redundant to do a separate m/$pat/ check.

[bobf]

it's redundant to do a separate m/$pat/ check

You are absolutely correct, of course. I started playing with patterns that would have required the extra check (because the ones used in s/// and m// were different), but I failed to remove the extra code after changing my approach. I added a note to my original reply but left the crufty code to avoid confusing future readers of this thread.