Hi all, Ok, I've got the Farari out of the garage, in to gear, and even driven it slowly around the block, but every time I put my foot down it just stalls. I'm trying to write a non trivial gui in Haskell. At the moment I'm using Hugs, and rapidly coming to the conclusion that I should be using something else such as GHC. As I see it the problem is basically that of tail recursion removal or as David Bergman calls it "last call optimisation". Specifically: David Bergman wrote
It is easy to get the feeling that the recursive call in
recurse = do { f x ; recurse }
is the last one, but this is just an illusion of the iterative layout of "do". Sometimes the monads lure us into old iterative thought patterns...
Taking away the syntactic sugar, we end up with
recurse = f x >> recurse
This reveals the fact that there can be no last call optimization, because the last call is ">>".
In response Richard Uhtenwoldt echoed my own thoughts ...
What do you mean by this? Do you mean that that an implementation cannot execute arbitrarily many iterations/recursions of that last loop/definition in constant space?
And also said ...
If that's what you mean, you are wrong. GHC does that. The IO monad would be pretty damned useless for actual work if implementations did not do that!
So, my problem is that I find that my program crashes with "garbage collector can't collect enough memory" after about 64 Million output operations. What's really annoying is that I can write the whole thing *recursively* in C in a very "functional" manner, and it works just fine. As I see it the problem is that >> and >>= are functions and David is right about the "not the last call" problem. But, Richard is right that related optimisations should be possible in Haskell, and if not then you can kiss the whole load good by and go back to system programming in C. In particular I would claim that the definition: recurse = f x >>= recurse is essentially using >>= as a proxy temporal execution handler. So in the above definition the call to recurse *is* a "last-call", at least according to >>=. I'm probably saying that in a rather unorthodox manner, but I hope my basic intention is clear. In fact we can see >> in Haskell as rather kin to ; in C (Or perhaps it should be >>=, since ; does transfer the state to the subsequent computation). So, I've loaded GHC and I'm looking to use it instead (I expected to eventually anyway), but does this solve my problem? Or have I misunderstood something here? Also ... I've been using the graphics libs with HUGS, but I can't find the equivalent in GHC ... what is the recomended library for writing GUIs in GHC Haskell? And where do I get it? Thanks in advance ... Bruce (IIMS, Massey at Albany). ps: I've also been looking at Fudgets, but the code seems a bit cranky.