gistfile1.txt

type family SExprExt (ext :: k1) (f :: k2)  = (r :: (* -> *)) | r -> ext where
  SExprExt ('[] :: [* -> *]) f = Union (MapList ('[] :: [* -> *]) f)
  SExprExt r                 f = Union (MapList r                 f)

class (Functor (SExprExt ext f), Foldable (SExprExt ext f), Traversable (SExprExt ext f)) =>  SimpleExprExtension ext f a where
  functorWitness :: p ext f a -> Dict (Functor (SExprExt ext f))
  functorWitness _ = Dict
  foldableWitness :: p ext f a -> Dict (Foldable (SExprExt ext f))
  foldableWitness _ = Dict
  traversableWitness :: p ext f a -> Dict (Traversable (SExprExt ext f))
  traversableWitness _ = Dict



type family MapList (l :: [ * -> * ]) f  = (r :: [* -> *] ) | r -> l  where
  MapList '[] f = '[]
  MapList (ext ': rest) f = (SExprExt ext f) ': MapList rest f

type MapConstraint constr l f = ConstrainedMembers constr (MapList l f)

instance (Functor (SExprExt ext f), Foldable (SExprExt ext f), Traversable (SExprExt ext f)) => SimpleExprExtension ext f a