Some questions first: What's the type of this function supposed to be? What's the type of unsafeCompare? How is the data type with NilFL and :>: defined?
-- ryan On Mon, Jan 12, 2009 at 5:43 AM, Rob Hoelz <r...@hoelzro.net> wrote: > Forwarding to Haskell Cafe per Eric's suggestion. > > Begin forwarded message: > > Date: Sun, 11 Jan 2009 23:01:31 -0600 > From: Rob Hoelz <r...@hoelzro.net> > To: darcs-de...@darcs.net > Subject: [darcs-devel] "Inferred type is less polymorphic than > expected" and type witnesses > > > Hello again, Darcs users and developers, > > As I mentioned in my last e-mail, I'm working on > http://bugs.darcs.net/issue291. It's actually gone pretty well, and I > feel I'm just about finished (I've done all but sorting out the > changes after leaving the editor), only I've encountered the compiler > error you see in the subject of this message. This error only appears > when compiling with witnesses. Here's the source for the function > that it's complaining about: > > compare_changes_with_old (x :>: xs) (y :>: ys) = > case compare_changes_with_old xs ys of > nx :> ny -> if unsafeCompare x y > then ((x :>: nx) :> ny) > else (NilFL :> (y :>: ys)) > compare_changes_with_old NilFL NilFL = (NilFL :> NilFL) > compare_changes_with_old NilFL ys@(_ :>: _) = (NilFL :> ys) > compare_changes_with_old x@(_ :>: _) NilFL = (NilFL :> NilFL) > > Now, I have two questions: > > 1) What exactly does this error mean, and how do I get around it? > 2) What are witness types, and what are they used for? > > I will gladly accept links to fine manuals as answers to either > question, but simple explanations would be nice. =D I thought I > understood Haskell pretty well, but existentially qualified types have > thrown me for a loop. > > Thanks much, > Rob Hoelz > _______________________________________________ > darcs-devel mailing list (AUTOMATIC POSTINGS ONLY PLEASE!) > darcs-de...@darcs.net > http://lists.osuosl.org/mailman/listinfo/darcs-devel > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
