+Note [Closure conversion]
+~~~~~~~~~~~~~~~~~~~~~~~~~
+We treat (\x. C p q) as a high-score candidate in the letrec scoring algorithm.
+The immediate motivation came from the result of a closure-conversion transformation
+which generated code like this:
+
+ data Clo a b = forall c. Clo (c -> a -> b) c
+
+ ($:) :: Clo a b -> a -> b
+ Clo f env $: x = f env x
+
+ rec { plus = Clo plus1 ()
+
+ ; plus1 _ n = Clo plus2 n
+
+ ; plus2 Zero n = n
+ ; plus2 (Succ m) n = Succ (plus $: m $: n) }
+
+If we inline 'plus' and 'plus1', everything unravels nicely. But if
+we choose 'plus1' as the loop breaker (which is entirely possible
+otherwise), the loop does not unravel nicely.
+
+