Just write it as two mutually recursive functions: 

$_ = "ABCOPCOGNHVCOHL"; 
my $P = sub { my($p, $q, $e, @s) = @_; $e, @s ? &{"C" ne $e ? $p : $q}
+($p, $q, @s) : () }; 
my $Q = sub { my($p, $q, $e, @s) = @_; ("O" ne $e ? () : "/"), &$p($p,
+ $q, $e, @s) }; 
print join "", &$P($P, $Q, split //), "\n";

[download]
(Don't take this answer seriously.)

In reply to Re: How to insert a "/" within a string? by ambrus
in thread How to insert a "/" within a string? by rsvp1920

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