All,
A little over 4 years ago, I wrote Merge Algorithm (Combining Sorted Lists). At the time, I was trying to find something useful to do for the community and was drinking the functional koolaid. As I indicated in the node:

"The code lacks a user defined option for handling duplicates and is likely buggy."

Additionally, ikegami pointed out a poor API choice with an aesthetic suggestion on fixing it. I had already lost interest but recently had a need for this and found out that it was in fact very buggy (2 bugs corrected and commented below). 
sub gen_merger {
    my ($list, $fetch, $compare, $finish) = @_;
    my @item = map $fetch->($_), @$list;
    
    my $done;
    return sub {
        return $finish if $done;        
        my $idx  = first {$item[$_] ne $finish} 0 .. $#item;
        my $next = $item[$idx];
        for ($idx + 1 .. $#item) {
            next if $item[$_] eq $finish;
            my $result = $compare->($next, $item[$_]);
            #$next = $item[$_] if $result == 1;
            # Need to keep track of which one we use not just value
            ($idx, $next) = ($_, $item[$_]) if $result == 1;
        }
        $item[$idx] = $fetch->($list->[$idx]);
        #$done = 1 if ! first {$item[$_] ne $finish} $idx .. $#item;
        # First element of array is 0 so use defined instead of truth
        $done = 1 if ! defined first {$item[$_] ne $finish} $idx .. $#
+item;
        return $next;
    };
}

[download]

Like then, I was being lazy. I would normally lean on sort -m but I need a custom compare routine and was going to throw away the code after the file was merged. After running for a few minutes, it complained "Out of memory!". I had already wasted enough time and just wrote a procedural version but as I look at the code, I can't figure out where the memory leak is. In case you are thinking it might be in the calling code, I used it exactly as the file handle example.

In case it matters, I was using the stock perl 5.8.2 that ships with AIX 5.3.

Cheers - L~R

In reply to Help Diagnosing Memory Leak by Limbic~Region

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