It's true that parentheses are very overloaded in Perl, and do many things. In the specific cases you mention, though, it's not so bad:

• ( ) create a list,
• { } create a hash,
• [ ] create an array.

So when you say:

my %hash = (fun => 'Simpsons')
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You're creating a two element list, and assigning that to %hash. However, when you say:

my $hash = { fun => 'Simpsons' }
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You're creating a two-element anonymous hash, and storing a reference to it in $hash (note the $ sigil, as opposed to the % sigil in the previous example).

The simple, though inexact, way to remember is that if you're assiging to a hash or an array:

%hash = ...
@array = ...
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You should have a list, which are surrounded by parens. But if you're assigning to a scalar:

$hash = ...
$array = ...
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You should have an anonymous array or an anonymous hash, which are surrounded by brackets or curlies.

This isn't exactly right. In fact, you can assign an anonymous hash as an element of another hash, which is what your %bad_hash = { ... } is doing. And assigning a list to a scalar isn't an error, but it won't do what your examples are trying to show. What I wrote is just a simple guideline to get you through until you're comfortable with the underlying concepts.

HTH