Just for info, GHC currently disallows a class decl like
class Foo a b => Baz b where ...
on the grounds that 'a' is isn't mentioned in the 'Baz b'
part. Arguably, if Foo has a FD b->a then it should be OK.
But currently it's rejected.
Simon
| -----Original Message-----
| From: Iavor S. Diatchki [mailto:diatchki@cse.ogi.edu]
| Sent: 10 December 2001 23:19
| To: hugs-bugs(a)haskell.org
| Subject: modules & functional dependencies?
|
|
| hi
|
| i seem to have stumbled upon a bug which somehow seems to be
| realted to
| the module system and functional dependencies. attached are
| four files (sorry about that, but it seems to happen when the
| class and instance are in
| different modules), 2 files per example.
|
| when Bug1 is loaded, no error is reported (although it should
| have been). if i edit the file (say just add a blank line)
| using the :e feature, then an
| error is reported, but seems like the wrong error - it says
| ERROR "Bug1.hs":6 - Illegal type in class constraint while if
| i just move the class to the same module, i get the correct
| error ERROR "Bug1.hs":8 - Undefined type variable "t'" (GHC
| comes up with this same error)
|
| when Bug2 is loaded i get the error:
| INTERNAL ERROR: inheritFundeps - predicate failed to match
| it's own head!
|
| although these messages dont seem related it seems like their
| cause is
| common. i am using the vesrion of hugs from the CVS from
| about 2 weeks ago (doesnt seem to have a number it just says YYMMDD)
|
| bye
| iavor
|
|
