Fix Trac #3437: strictness of specialised functions
'lilac' helpful pin-pointed a space leak that was due to a specialised function being insufficiently strict. Here's the new comment in SpecConstr: Note [Transfer strictness] ~~~~~~~~~~~~~~~~~~~~~~~~~~ We must transfer strictness information from the original function to the specialised one. Suppose, for example f has strictness SS and a RULE f (a:as) b = f_spec a as b Now we want f_spec to have strictess LLS, otherwise we'll use call-by-need when calling f_spec instead of call-by-value. And that can result in unbounded worsening in space (cf the classic foldl vs foldl') See Trac #3437 for a good example. The function calcSpecStrictness performs the calculation.