The difference is that (generally in programming languages) a type is something defined with a name while a constraint is ad-hoc. If you use types for everythin

The difference is that (generally in programming languages) a type is something defined with a name while a constraint is ad-hoc. If you use types for everything you'll have to write a whole lot: this variable is a Size3List, this one is a Size5List, this one is a PrimePowersList.