perl-Specio

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.