* What are the relative advantages of Hugs and GHC, beyond the obvious (Hugs is smaller and easier for people not named Simon to modify, while GHC is a real compiler and has the most up-to-date hacks to the type checker)? Do people generally use one or the other for everything, or are they similar enough to use Hugs at some moments and GHC at others?
I just completely redesigned our first year undergraduate Haskell module and considered moving from Hugs to GHC. Because most students have Windows at home I don't consider installation a problem for GHC. GHC is the compiler for serious Haskell development. While this is not needed for beginners, I believe it demonstrates better to students that Haskell is not just an academic toy language. The error messages of GHC are generally better than those of Hugs; unfortunately GHC produces very bad parse errors and beginners tend to make lots of those (however, Hugs has the infamous unexpected semicolon error message). Hugs stops after the first error message, while GHC usually reports many errors. I think that for beginners the long list produced by GHC is more frustrating and they only repair one error at a time anyway. Hugs is also quicker in reporting an error. I also do not like that GHC exposes non-Haskell 98 features: if you type :t length you get length :: forall a. [a] -> Int. "forall" is not Haskell 98. So because of such a list of slightly beginner-unfriendly features I decided to stay with Hugs for this year. I might revise this next year, especially if GHC improves (I should ask Simon&Simon about these issues...) I also like the built-in HOOD of Hugs that makes "observe" polymorphic. However, I'll probably give up my original plan of using it in lectures to observe functions and thus get a better intuitive feeling for functions as mappings from inputs to results.
I've clearly got a lot to learn about space usage in Haskell... can someone give me a hint about what is the problem here and how it might best be corrected?
I'm glad to see Ross' explanation that the space problem is caused by the library, because your code looked fine to me. I'm constantly surprised hearing from so many people about their space problems. I cannot remember having space problems with my programs. I don't know what everybody else is doing wrong :-) I do disagree with people recommending strictness annotations (seq etc). In contrast, I make my programs as lazy as possible. Actually I just remember once adding 'seq' to my pretty printing library to ensure it had the space complexity I wanted (not that there was a problem in practice). However, shortly afterwards I realised that I could rewrite that part in a way that made 'seq' superfluous, was shorter, nicer, and probably even slightly more efficient. Ciao, Olaf