+
+-- "seq" is defined a bit wierdly (see below)
+--
+-- The reason for the strange "0# -> parError" case is that
+-- it fools the compiler into thinking that seq is non-strict in
+-- its second argument (even if it inlines seq at the call site).
+-- If it thinks seq is strict in "y", then it often evaluates
+-- "y" before "x", which is totally wrong.
+--
+-- Just before converting from Core to STG there's a bit of magic
+-- that recognises the seq# and eliminates the duff case.
+