Documentation

Generically derive CBLen type family instances.

A type having a valid CBLen instance usually indicates one of the following:

• it's a primitive, or extremely simple
• it holds size information in its type
• it's constructed from other constant byte length types

The first two cases must be handled manually. The third case is where Haskell generics excel, and the one this module targets.

You may derive a CBLen type generically for a non-sum type with

instance IsCBLen a where type CBLen a = CBLenGenericNonSum a

You may attempt to derive a CBLen type generically for a sum type with

instance IsCBLen a where type CBLen a = CBLenGenericSum w a

As with other generic sum type handlers, you must provide the type used to store the sum tag for sum types. That sum tag type must have a CBLen, and every constructor must have the same CBLen for a CBLen to be calculated. Not many types will fit those criteria, and the code is not well-tested.