+-- | Build the PA dictionary for some type and hoist it to top level.
+-- The PA dictionary holds fns that convert values to and from their vectorised representations.
+buildPADict
+ :: TyCon -- ^ tycon of the type being vectorised.
+ -> TyCon -- ^ tycon of the type used for the vectorised representation.
+ -> TyCon --
+ -> SumRepr -- ^ representation used for the type being vectorised.
+ -> VM Var -- ^ name of the top-level dictionary function.