$ perl -Mstrict -Mwarnings -le '
    package myDebugger;
    my $debugger;
    sub GetInstance { defined $debugger ? $debugger : DebuggerInit() }
    sub DebuggerInit { $debugger = "singleton" }
    # a typo later in your code (perhaps "$debug = 0;" was intended)
    my $debug = 1;
    # ...
    $debugger = 0;

    package main;
    print myDebugger::GetInstance();
    print myDebugger::GetInstance();
'
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