Comment warning about transparent newtypes

diff --git a/compiler/types/TyCon.lhs b/compiler/types/TyCon.lhs
index 84d16e0..7d11482 100644 (file)
--- a/compiler/types/TyCon.lhs
+++ b/compiler/types/TyCon.lhs
@@ -256,6 +256,8 @@ data AlgTyConRhs
                                -- See Note [Newtype coercions]
                                -- Invariant: arity = #tvs in nt_etad_rhs;
                                --      See Note [Newtype eta]
+                               -- Watch out!  If any newtypes become transparent
+                               -- again check Trac #1072.
 
        nt_etad_rhs :: ([TyVar], Type) ,
                        -- The same again, but this time eta-reduced