+ checking. For example, {\tt length} has type
+
+ {\tt length :: forall a. [a] -> Int}
+
+ and the list datacon for the empty list has type
+
+ {\tt [] :: forall a. [a]}
+
+ In order to compose these two terms as {\tt length []} a type
+ application is required, but there is no constraint on the
+ choice. In this situation GHC uses {\tt Any}: