Tomasz Zielonka
Thank you. It works for me too, but I don't understand why and how ;-)) Could you explain?
I'm a bit puzzled by this discussion, as strictness of FiniteMaps have rarely been (perceived to be?) a problem for me.
Scott's solution forces (lookupFM a' x) to head normal form (or is it weak head normal form). This means that the value of type (Maybe v) is evaluated as much that it is known whether it is Nothing, Just _ or _|_ (bottom). This is probably enough to evaluate the path from FiniteMap's tree root to x.
If you insert a value into a FiniteMap, isn't the key necessarily evaluated anyway? Or is the problem that you can get a long chain of unevaluated 'addToFM's? The trick would then be to evaluate the FM now and then (e.g. using a strict fold).
However (lookupFM a' x) in head normal form can be still something like this: Just
I thought simply forcing evaluation of the value before inserting would do it (i.e. something like v `seq` addToFm fm k v (modulo v needing deeper seq'ing, that is) Am I missing something? -kzm -- If I haven't seen further, it is by standing in the footprints of giants