The solution provided in 1st reply is correct, and also there is another way to fix this problem: to put a '&' before those function calls, do something like:

&func_abc($param_abc);
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I made a simple testing program, which has three parts:

sub say_something($); #prototype

sub say_something { #sub body
    print "I got ".shift()."\n";
}

say_something("an apple");# call the sub.
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I played with it, with different sequences of the three parts(there are other combinations, you can play with them):

1. proto->body->call, this fine.
2. proto->call->body, this is also fine.
3. call->proto->func, this is not fine, and got the error msg you got.
4. call with &->proto->func, it back to okay.