On Saturday 30 July 2005 03:54, Thomas Jäger wrote:
You're probably refering to the version where you omit the type signatures of both 'printer' and 'printCatalog'. Here the situation is different because the compiler needs to infer the types and not just check. In the explicitely typed version, 'printCatalog' is used polymorphically, i.e. the 'c' is instantiated to different types during the recursive call. Thus the example needs polymorphic recursion, for which type inference is known to be undecidable. It is therefore reasonable that ghc (as well as hugs) can't compile the code (in fact, I guess type inference will assume that both contexts are equal).
Hmm. I am not sure I understand this. Are you saying, that the second error causes the first one? Thus, everything is caused by 'printer' being recursively defined? Are contexts with differing length in a recursive definition ok in Hugs (as in the latest version of ghc) and therefore with Hugs I don't get the first message either? Ben