When we pass the default method binding to the type checker, it must
look like op2 = e
not $dmop2 = e
-otherwise the "$dm" stuff comes out in the interface file. So we
-typecheck the former, and wrap it in a let, thus
+otherwise the "$dm" stuff comes out error messages. But we want the
+"$dm" to come out in the interface file. So we typecheck the former,
+and wrap it in a let, thus
$dmop2 = let op2 = e in op2
This makes the error messages right.