+First, two special cases. We mangle cases involving
+ par# and seq#
+inthe scrutinee.
+
+Up to this point, seq# will appear like this:
+
+ case seq# e of
+ 0# -> seqError#
+ _ -> <stuff>
+
+This code comes from an unfolding for 'seq' in Prelude.hs.
+The 0# branch is purely to bamboozle the strictness analyser.
+For example, if <stuff> is strict in x, and there was no seqError#
+branch, the strictness analyser would conclude that the whole expression
+was strict in x, and perhaps evaluate x first -- but that would be a DISASTER.
+
+Now that the evaluation order is safe, we translate this into
+
+ case e of
+ _ -> ...
+
+This used to be done in the post-simplification phase, but we need
+unfoldings involving seq# to appear unmangled in the interface file,
+hence we do this mangling here.
+
+Similarly, par# has an unfolding in PrelConc.lhs that makes it show
+up like this:
+
+ case par# e of
+ 0# -> rhs
+ _ -> parError#
+
+
+ ==>
+ case par# e of
+ _ -> rhs
+
+fork# isn't handled like this - it's an explicit IO operation now.
+The reason is that fork# returns a ThreadId#, which gets in the
+way of the above scheme. And anyway, IO is the only guaranteed
+way to enforce ordering --SDM.
+
+
+\begin{code}
+coreExprToStgFloat env
+ (Case scrut@(Con (PrimOp SeqOp) [Type ty, e]) bndr alts) dem
+ = coreExprToStgFloat env (Case e new_bndr [(DEFAULT,[],default_rhs)]) dem
+ where
+ (other_alts, maybe_default) = findDefault alts
+ Just default_rhs = maybe_default
+ new_bndr = setIdType bndr ty
+ -- NB: SeqOp :: forall a. a -> Int#
+ -- So bndr has type Int#
+ -- But now we are going to scrutinise the SeqOp's argument directly,
+ -- so we must change the type of the case binder to match that
+ -- of the argument expression e. We can get this type from the argument
+ -- type of the SeqOp.
+
+coreExprToStgFloat env
+ (Case scrut@(Con (PrimOp ParOp) args) bndr alts) dem
+ | maybeToBool maybe_default
+ = coreExprToStgFloat env scrut (bdrDem bndr) `thenUs` \ (binds, scrut') ->
+ newEvaldLocalId env bndr `thenUs` \ (env', bndr') ->
+ coreExprToStg env' default_rhs dem `thenUs` \ default_rhs' ->
+ returnUs (binds, mkStgCase scrut' bndr' (StgPrimAlts (idType bndr') [] (StgBindDefault default_rhs')))
+ where
+ (other_alts, maybe_default) = findDefault alts
+ Just default_rhs = maybe_default
+\end{code}
+
+Now for normal case expressions...
+