[Haskell-cafe] Skolems!

[Jan Stolarek]

> A quick clarification. It s trac still the location to submit bugs or is
> Phabricator more appropriate?
Trac is still the place to submit bugs. Once a bug-fix is ready we use Phabricator to code-review 
the patch.

Janek

>
> On Mon, Mar 2, 2015 at 1:49 PM, evan at evan-borden.com <
>
> evan at evanrutledgeborden.dreamhosters.com> wrote:
> > Thanks Richard, will do.
> >
> > On Mon, Mar 2, 2015 at 1:12 PM, Richard Eisenberg <eir at cis.upenn.edu>
> >
> > wrote:
> >> This is admittedly a dark corner of the inference algorithm, but perhaps
> >> these examples can shed some light. Post a bug report!
> >>
> >> Thanks for creating nice, small examples.
> >>
> >> Richard
> >>
> >> PS: I offer no strong guarantees that you've found bugs here... but in
> >> any case, posting a bug report gets more serious attention than a
> >> Haskell-cafe post.
> >>
> >> On Feb 27, 2015, at 1:23 PM, "evan at evan-borden.com" <
> >>
> >> evan at evanrutledgeborden.dreamhosters.com> wrote:
> >> > An extension of the message Tom sent a little while back, we've
> >>
> >> discovered a more in depth example of this possible GHC bug. It is
> >> exacerbated by GADTs, but can be fixed with NoMonoLocalBinds. Without
> >> GADTs and just leveraging ExistentialQuanitification it works fine.
> >> We've included a pretty exhaustive set of examples.
> >>
> >> >   {-# LANGUAGE ExistentialQuantification, GADTs #-}
> >> >
> >> >   {- removing MonoLocalBinds fixes all of these errors
> >> >   {-# LANGUAGE ExistentialQuantification, GADTs, NoMonoLocalBinds #-}
> >> >   -}
> >> >
> >> >   module PossibleGHCBug where
> >> >
> >> >   data SumType = SumFoo | SumBar
> >> >
> >> >   class SomeClass a where
> >> >     someType :: a -> SumType
> >> >
> >> >   data SomeExistential = forall a. SomeClass a => SomeExistential a
> >> >
> >> >   noError :: String -> [SomeExistential] -> String
> >> >   noError n st = n ++ concatMap cname st
> >> >     where cname (SomeExistential p) = d p
> >> >
> >> >           d p = c $ someType p
> >> >
> >> >           c p = case p of
> >> >                     SumFoo -> "foo"
> >> >                     _ -> "asdf"
> >> >
> >> >   noError2 :: String -> [SomeExistential] -> String
> >> >   noError2 n st = n ++ concatMap cname st
> >> >     where cname (SomeExistential p) = d p
> >> >
> >> >           d p = c $ someType p
> >> >
> >> >           c :: SumType -> String
> >> >           c p = case p of
> >> >                     SumFoo -> "foo"
> >> >                     _ -> "asdf" ++ n
> >> >
> >> >   noError3 :: String -> [SomeExistential] -> String
> >> >   noError3 n st = n ++ concatMap cname st
> >> >     where cname (SomeExistential p) = d p
> >> >
> >> >           d :: SomeClass a => a -> String
> >> >           d p = c $ someType p
> >> >
> >> >           c p = case p of
> >> >                     SumFoo -> "foo"
> >> >                     _ -> "asdf" ++ n
> >> >
> >> >
> >> >   partialTypedError :: String -> [SomeExistential] -> String
> >> >   partialTypedError n st = n ++ concatMap cname st
> >> >     where cname :: SomeExistential -> String
> >> >           cname (SomeExistential p) = d p
> >> >
> >> >           d p = c $ someType p
> >> >
> >> >           c p = case p of
> >> >                     SumFoo -> "foo"
> >> >                     _ -> "asdf" ++ n
> >> >
> >> >   fullError :: String -> [SomeExistential] -> String
> >> >   fullError n st = n ++ concatMap cname st
> >> >     where cname (SomeExistential p) = d p
> >> >
> >> >           d p = c $ someType p
> >> >
> >> >           c p = case p of
> >> >                     SumFoo -> "foo"
> >> >                     _ -> "asdf" ++ n
> >> >
> >> >   justNError :: String -> [SomeExistential] -> String
> >> >   justNError n st = n ++ concatMap cname st
> >> >     where cname (SomeExistential p) = d p
> >> >
> >> >           d p = c $ someType p
> >> >
> >> >           c p = case p of
> >> >                     SumFoo -> "foo"
> >> >                     _ -> n
> >> >
> >> >   ignoreNError :: String -> [SomeExistential] -> String
> >> >   ignoreNError n st = n ++ concatMap cname st
> >> >     where cname (SomeExistential p) = d p
> >> >
> >> >           d p = c $ someType p
> >> >
> >> >           c p = case p of
> >> >                     SumFoo -> "foo"
> >> >                     _ -> fst ("foo", n)
> >> >
> >> >
> >> > _______________________________________________
> >> > Haskell-Cafe mailing list
> >> > Haskell-Cafe at haskell.org
> >> > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe



---
Politechnika Łódzka
Lodz University of Technology

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