Hint: the trick is to check if the value of each key is a reference to a hash or array or ... and if so, just expand this value appropriately. It is probably a good candidate for some recursive code.

From the docs:

ref EXPR

ref

Returns a non-empty string if EXPR is a reference, the empty string otherwise. If EXPR is not specified, $_ will be used. The value returned depends on the type of thing the reference is a reference to. Builtin types include:

• SCALAR
• ARRAY
• HASH
• CODE
• REF
• GLOB
• LVALUE

If the referenced object has been blessed into a package, then that package name is returned instead. You can think of ref as a typeof operator.

if (ref($r) eq "HASH") {
            print "r is a reference to a hash.\n";
        }
        unless (ref($r)) {
            print "r is not a reference at all.\n";
        }
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