My solution is not really a competitor, since I'm not that
familiar with Perl Golf customs, so bear with me.
use strict;
sub f {
my ($a,$b,$m,$n) = @_;
my (@r) = ();
my $l = " $a! $b";
while($l =~ s/(.*?)(( \w+){$m,$n} )(.*!.*\2.*)/ $1 =$4/) {
push @r, $2;
};
@r
};
Why I'm posting this at all is, that a previous version
exhibited unanticipated (by me, that is) behaviour :
# Previous version :
my $l = " $a! $b";
while($l =~ s/(.*)(( \w+){$m,$n} )(.*!.*\2.*)/ $1 =$4/) {
push @r, $2;
};
@r
That version only found the $m-word
matches, because the greedy (.*) at the beginning
forced the RE engine to work its way backwards through
the string. As soon as I sacrificed another character,
this problem went away. I haven't given the golfing much
thought (at work, I can only think about concepts, not
byte-fiddle with REs without raising suspicions ... ).