> The interaction between solving class constraints and equalities with type
> families is currently rather ad hoc.
>
FYI
*September 2008*
*Unified Type Checking for Type Classes and Type Families*, T. Schrijvers,
M. Sulzmann. Presented at the ICFP 2008 poster session
(pdf available on Tom's home
As Lennart wrote, with UndecideableInstances all bets are off.
Concerning the fixed-depth recursion stack. It is currently only used
for the simplification of class instance declarations, but if
improvement rules are involved (either FDs or TFs) that check will not
catch all cases anyway.
-- Uncommenting the line below causes the typechecker to loop (GHC 6.10.1,
Windows)
--test = f Zero
Is this expected behavior or a bug?
The call f Zero requires a co-inductive proof of the type class
constraint (F Nat):
F Nat <=> Vieweable Nat /\ F' (View Nat)
<=> True
Hello Lennart,
Yes, but according to the manual (
http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensions.html#undecidable-instances),
"Termination is ensured by having a fixed-depth recursion stack". So I would
expect at least termination, which I'm not getting (but I guess
Turning on UndecidableInstances is the same as saying: OK typechcker,
you can loop if I make a mistake.
I've not looked closely at your code, but if you turn on that flag,
looping is probably not a bug.
-- Lennart
2008/12/4 José Pedro Magalhães <[EMAIL PROTECTED]>:
> Hello all,
>
> Please consi
Hello all,
Please consider the following code:
{-# OPTIONS -Wall #-}
> {-# LANGUAGE FlexibleContexts #-}
> {-# LANGUAGE FlexibleInstances#-}
> {-# LANGUAGE TypeOperators#-}
> {-# LANGUAGE TypeFamilies #-}
> {-# LANGUAGE OverlappingInstances #-}
> {-# LANGUA
