John Peterson wrote: > The downside of Haskell is that none of the regular implementations > (ghc, hugs) are really right for this level of student. Type > inference is an especially nasty problem. There also a number of > gotcha's lurking in the language that cause problems.
For exactly these reasons we have implemented Helium; not for replacing Haskell (we're very happy with Haskell), but for *learning* Haskell. There is no overloading, so types and type errors are easier to understand. The Helium compiler produces warnings for situations that are probably incorrect. I've found myself look at a program with a comparable problem as the one below for fifteen minutes until I saw what was happening (please look at the program with a non-proportional font like Courier for optimal confusion): filterr :: (a -> Bool) -> [a] -> [a] filterr p [] = [] fi1terr p (x:xs) = if p x then x : filterr p xs else filterr p xs Hugs, which we used for teaching, doesn't say a word. GHC does give helpful warnings if you pass the -Wall flag. Helium says: (2,9): Variable "p" is not used (3,1): Missing type signature: fi1terr :: (a -> Bool) -> [a] -> [a] (3,1): Suspicious adjacent functions "fi1terr" and "filterr" I'm curious what the other "gotcha's" are that John refers to because it might give us inspiration for more warnings/language design decisions. Arjan http://www.cs.uu.nl/~afie/helium/ _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
