| You probably mean
| J. Sparud, "Fixing Some Space Leaks without a Garbage Collector",
FPCA'93.
| http://citeseer.ist.psu.edu/sparud93fixing.html
Indeed.
| as implemented in hbc. It is also possible to use Wadler's
| garbage-collector fix for this space leak, as implemented in nhc98.
| P Wadler, "Fixing a Space Leak with a Garbage Collector", SP&E
Sept 1987.
|
| When the GC discovers a selector function applied to an evaluated
| argument, it "evaluates" the selector on-the-fly by just swizzling
| pointers. It needs some co-operation from the compiler to make
| selector functions look obvious, but that isn't too difficult.
GHC does this, but it does not always work. What starts as
let x = fst t in
let h = case x of { True -> 1; False -> 2 } in
...
may become
let h = case t of { (x,_) -> case x of {True->1;False->2} }
...
and now there is no selector thunk any more. So the selector stuff is
fragile to otherwise-valuable optimisations. And that's what's happening
in this case. A non-optimising compiler is fine.
Simon
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