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    sub explain {
        my $val = shift;
        print "Numeric value = ", 0+$val, "\n";
        print "String value = \"$val\"\n";
        print "Truth value = ", $val ? "true\n" : "false\n";
    }

    # explain("23skidoo");
    Numeric value = 23
    String value = "23skidoo"
...
    Numeric value = 0
    String value = ""
    Truth value = false

[robin@robin robin]$ perl -wle 'print 0+"23skidoo"'
Argument "23skidoo" isn't numeric in addition (+) at -e line 1.
23

[robin@robin bits & pieces]$ perl -wle 'print 23+"0 but true"'
23

    # explain([1,2,3]);
    Numeric value = 25616
    String value = "ARRAY(0x6410)"
    Truth value = true

    my $foo = *bar;
    our $bar = "hello\n";
    our @bar = ("Hello again!\n");
    print $$foo, @$foo;
    explain($foo);

    hello
    Hello again!
    Numeric value = 0
    String value = "*main::bar"
    Truth value = true

    # explain(bless {}, "SomePackage");
    Numeric value = 25616
    String value = "SomePackage=HASH(0x6410)"
    Truth value = true

    explain(bless {}, "SomePackage");
    package SomePackage;
    use overload '""'   => sub {'string value'};
    use overload '0+'   => sub {23};
    use overload 'bool' => sub {""};
    use overload fallback => 1;

    Numeric value = 23
    String value = "string value"
    Truth value = false

    Numeric value = 0
    String value = "string value"
    Truth value = true

    explain(bless {}, "SomePackage");
    package SomePackage;
    use overload '""'   => sub {''};
    use overload '0+'   => sub {23};
    use overload fallback => 1;

    Numeric value = 23
    String value = ""
    Truth value = true

    explain(bless {}, "SomePackage");
    package SomePackage;
    use overload '""'   => sub { '' };
    use overload '0+'   => sub {'00'};
    use overload fallback => 1;