The 'Specio' distribution provides classes for representing type
constraints and coercion, along with syntax sugar for declaring them.

Note that this is not a proper type system for Perl. Nothing in this
distribution will magically make the Perl interpreter start checking a
value's type on assignment to a variable. In fact, there's no built-in way
to apply a type to a variable at all.

Instead, you can explicitly check a value against a type, and optionally
coerce values to that type.