Generic.Data.Internal.Error

Error messages.

Warning

This is an internal module: it is not subject to any versioning policy, breaking changes can happen at any time.

If something here seems useful, please report it or create a pull request to export it from an external module.

Documentation

type family HasSum f where ...

Equations

HasSum V1 = 'False

HasSum U1 = 'False

HasSum (K1 i c) = 'False

HasSum (M1 i c f) = HasSum f

HasSum (f :*: g) = HasSum f || HasSum g

HasSum (f :+: g) = 'True

class Assert (pred :: Bool) (msg :: ErrorMessage)

Instances

(TypeError msg :: ()) ~ '() => Assert 'False msg

Defined in Generic.Data.Internal.Error

Assert 'True msg

Defined in Generic.Data.Internal.Error

type AssertNoSum (constraint :: Type -> Constraint) a = Assert (Not (HasSum (Rep a))) (((('Text "Cannot derive " ':<>: 'ShowType constraint) ':<>: 'Text " instance for ") ':<>: 'ShowType a) ':<>: 'Text " due to sum type")

>>> :set -XDeriveGeneric -XDerivingVia
>>> import Generic.Data (Generically(..))
>>> :{
  data AB = A | B
    deriving stock Generic
    deriving Semigroup via Generically AB
:}
...
    • Cannot derive Semigroup instance for AB due to sum type
    • When deriving the instance for (Semigroup AB)