mk_eqn_help gla_exts new_or_data tycon deriv_tvs clas tys
------------------------------------------------------------------
+ -- data/newtype T a = ... deriving( C t1 t2 )
+ -- leads to a call to mk_eqn_help with
+ -- tycon = T, deriv_tvs = ftv(t1,t2), clas = C, tys = [t1,t2]
+
mk_eqn_help gla_exts DataType tycon deriv_tvs clas tys
| Just err <- checkSideConditions gla_exts tycon deriv_tvs clas tys
= bale_out (derivingThingErr clas tys tycon (tyConTyVars tycon) err)
-- We must pass the superclasses; the newtype might be an instance
-- of them in a different way than the representation type
-- E.g. newtype Foo a = Foo a deriving( Show, Num, Eq )
- -- Then the Show instance is not done via isomprphism; it shows
+ -- Then the Show instance is not done via isomorphism; it shows
-- Foo 3 as "Foo 3"
-- The Num instance is derived via isomorphism, but the Show superclass
-- dictionary must the Show instance for Foo, *not* the Show dictionary