+-- NB. It is tempting to think that casting a value to a type that it doesn't have is safe
+-- as long as you don't "do anything" with the value in its cast form, such as seq on it. This
+-- isn't the case: the compiler can insert seqs itself, and if these happen at the wrong type,
+-- Bad Things Might Happen. See bug #1616: in this case we cast a function of type (a,b) -> (a,b)
+-- to () -> () and back again. The strictness analyser saw that the function was strict, but
+-- the wrapper had type () -> (), and hence the wrapper de-constructed the (), the worker re-constructed
+-- a new (), with the result that the code ended up with "case () of (a,b) -> ...".