Make records work properly with type families

[ghc-hetmet.git] / compiler / basicTypes / MkId.lhs

diff --git a/compiler/basicTypes/MkId.lhs b/compiler/basicTypes/MkId.lhs
index 42515eb..c4618ca 100644 (file)
--- a/compiler/basicTypes/MkId.lhs
+++ b/compiler/basicTypes/MkId.lhs
@@ -493,6 +493,8 @@ mkRecordSelId tycon field_label
 
     con1       = head data_cons_w_field
     (univ_tvs, _, eq_spec, _, _, data_ty) = dataConFullSig con1
+       -- For a data type family, the data_ty (and hence selector_ty) mentions
+       -- only the family TyCon, not the instance TyCon
     data_tv_set        = tyVarsOfType data_ty
     data_tvs   = varSetElems data_tv_set
     field_ty   = dataConFieldType con1 field_label