+ = postSimplExpr body `thenPM` \ body' ->
+ -- Do *not* call postSimplExprEta here
+ -- We don't want to turn f = \x -> coerce t (\y -> f x y)
+ -- into f = \x -> coerce t (f x)
+ -- because then f has a lower arity.
+ -- This is not only bad in general, it causes the arity to
+ -- not match the [Demand] on an Id,
+ -- which confuses the importer of this module.