"Simon Peyton-Jones"
I had a look at this. It's an old chestnut: lazy pattern matching. You have let ((commands, s), x) = run (read iters) 5 in do ...do something with commands... print x
Trouble is, the 'x' hangs onto both components of the pair, even though it only needs one.
This lazy-pattern-matching leak is a well-known problem, to which I do not know a good solution. There was a paper from Chalmers about 8 years ago about building more cleverness into the compiler, but it amounted to extending Core with a lazy tuple binding. Fair enough, but quite a big addition to Core and one I've never done.
You probably mean J. Sparud, "Fixing Some Space Leaks without a Garbage Collector", FPCA'93. http://citeseer.ist.psu.edu/sparud93fixing.html 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. Regards, Malcolm