map generally takes simple expressions in the braces.

Why do you assign the return value of process() to a variable, if you don't do anything with it? Just invoke it as a routine:

$module->target($_);
$module->process();
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As for the memory leak, I suspect my is generating new variables for each array element, which aren't being released until map finishes. Try encapsulating the map code into a subroutine.... that will make fix the leak, I bet.

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