module containing GADTs no longer compiles in ghc 6.8.0
Hi I just tried to compile a project of mine that builds fine using ghc 6.6.1 and got many errors like this: src/HyLo/Formula/NNF.hs:247:48: GADT pattern match in non-rigid context for `Opaque' Tell GHC HQ if you'd like this to unify the context In the pattern: Opaque f' In the expression: \ (Opaque f') -> Opaque (Box r f') In the definition of `box': box = \ (Opaque f') -> Opaque (Box r f') I don't know what a "non-rigid context" is, nor if "I like this to unify the context" or not, but I would certainly be happy if I could get this module to compile again! :) For the record, I was using ghc-6.8.0.20070917. Please let me know if you need further information.... Thanks Daniel PS: On a side note, I found this error message to be kind of funny. It seems to indicate no real error but some sort of error-message-driven poll!
| PS: On a side note, I found this error message to be kind of funny. It seems | to indicate no real error but some sort of error-message-driven poll! That's exactly what it is, and you are the pollee. Nevertheless it's probably needlessly obscure. The point is this: you are doing case x of { ... } where the "..." has GADT patterns. But GHC doesn't know what type 'x' is. Usually type inference will suffice, but not for GADTs. Solution: use a type signature to tell GHC just what type x has. Example: f x = case x of ... give f a type signature f :: forall a. T a -> Int There ought to be a "contributed documentation" wiki page about GADTs here http://haskell.org/haskellwiki/GHC but there isn't yet. Would someone like to start one? sorry brevity, rushing to get to icfp Simon | -----Original Message----- | From: glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell-users-bounces@haskell.org] On | Behalf Of Daniel Gorín | Sent: 26 September 2007 17:34 | To: glasgow-haskell-users@haskell.org | Subject: module containing GADTs no longer compiles in ghc 6.8.0 | | Hi | | I just tried to compile a project of mine that builds fine using ghc 6.6.1 and | got many errors like this: | | src/HyLo/Formula/NNF.hs:247:48: | GADT pattern match in non-rigid context for `Opaque' | Tell GHC HQ if you'd like this to unify the context | In the pattern: Opaque f' | In the expression: \ (Opaque f') -> Opaque (Box r f') | In the definition of `box': | box = \ (Opaque f') -> Opaque (Box r f') | | I don't know what a "non-rigid context" is, nor if "I like this to unify the | context" or not, but I would certainly be happy if I could get this module to | compile again! :) | | For the record, I was using ghc-6.8.0.20070917. Please let me know if you need | further information.... | | Thanks | Daniel | | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users@haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Hi Simon, Thanks for your prompt response. Actually, the problem was with lambda patterns containing GADT constructors in let bindings and I guess GHC doesn't like that anymore. After replacing them with case statements everything compiles fine.... as long as I don't turn on -O2 optimizations :( This boiled-down example illustrates my problem:
{-# OPTIONS_GHC -fglasgow-exts #-} module T where
data T a where T :: T a -> T [a]
class C a where f :: a -> ()
instance C (T [a]) where f (T x@(T _)) = f x
$ ghc --make -c -Wall -O2 T [1 of 1] Compiling T ( T.hs, t/T.o ) ghc-6.8.0.20070917: panic! (the 'impossible' happened) (GHC version 6.8.0.20070917 for i386-unknown-linux): Template variable unbound in rewrite rule co_X6j{tv} [tv] [a{tv a5u} [sk], co_a5X{tv} [tv], a{tv a5Y} [sk], co_a60{tv} [tv], ds_d67{v} [lid]] [a{tv X5P} [sk], co_X6j{tv} [tv], a{tv X6l} [sk], co_X6o{tv} [tv], ds_X6w{v} [lid]] [TYPE a{tv a5Y} [sk], (main:T.T{v r5Q} [gid] @ a{tv a5u} [sk] @ a{tv a5Y} [sk] @ co_a60{tv} [tv] ds_d67{v} [lid]) `cast` (base:GHC.Prim.trans{(w) tc 34y} (main:T.T{tc r1} (base:GHC.Prim.right{(w) tc 34E} co_a5X{tv} [tv])) (base:GHC.Prim.trans{(w) tc 34y} (main:T.T{tc r1} (base:GHC.Prim.right{(w) tc 34E} (base:GHC.Prim.sym{(w) tc 34v} co_a5X{tv} [tv]))) (main:T.T{tc r1} co_a60{tv} [tv])) :: <pred>main:T.T{tc r1} a{tv a5u} [sk] ~ main:T.T{tc r1} [a{tv a5Y} [sk]])] [TYPE a{tv a5Y} [sk], wild_Xc{v} [lid] `cast` (base:GHC.Prim.trans{(w) tc 34y} (main:T.T{tc r1} (base:GHC.Prim.right{(w) tc 34E} co_a5X{tv} [tv])) (base:GHC.Prim.trans{(w) tc 34y} (main:T.T{tc r1} (base:GHC.Prim.right{(w) tc 34E} (base:GHC.Prim.sym{(w) tc 34v} co_a5X{tv} [tv]))) (main:T.T{tc r1} co_a60{tv} [tv])) :: <pred>main:T.T{tc r1} a{tv a5u} [sk] ~ main:T.T{tc r1} [a{tv a5Y} [sk]])] Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug Thanks Daniel On Wednesday 26 September 2007 13:55:10 Simon Peyton-Jones wrote:
| PS: On a side note, I found this error message to be kind of funny. It | seems to indicate no real error but some sort of error-message-driven | poll!
That's exactly what it is, and you are the pollee.
Nevertheless it's probably needlessly obscure. The point is this: you are doing case x of { ... } where the "..." has GADT patterns. But GHC doesn't know what type 'x' is. Usually type inference will suffice, but not for GADTs.
Solution: use a type signature to tell GHC just what type x has. Example:
f x = case x of ...
give f a type signature
f :: forall a. T a -> Int
There ought to be a "contributed documentation" wiki page about GADTs here http://haskell.org/haskellwiki/GHC but there isn't yet. Would someone like to start one?
sorry brevity, rushing to get to icfp
Simon
| -----Original Message----- | From: glasgow-haskell-users-bounces@haskell.org | [mailto:glasgow-haskell-users-bounces@haskell.org] On Behalf Of Daniel | Gorín | Sent: 26 September 2007 17:34 | To: glasgow-haskell-users@haskell.org | Subject: module containing GADTs no longer compiles in ghc 6.8.0 | | Hi | | I just tried to compile a project of mine that builds fine using ghc | 6.6.1 and got many errors like this: | | src/HyLo/Formula/NNF.hs:247:48: | GADT pattern match in non-rigid context for `Opaque' | Tell GHC HQ if you'd like this to unify the context | In the pattern: Opaque f' | In the expression: \ (Opaque f') -> Opaque (Box r f') | In the definition of `box': | box = \ (Opaque f') -> Opaque (Box r f') | | I don't know what a "non-rigid context" is, nor if "I like this to unify | the context" or not, but I would certainly be happy if I could get this | module to compile again! :) | | For the record, I was using ghc-6.8.0.20070917. Please let me know if you | need further information.... | | Thanks | Daniel | | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users@haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Hi Daniel, On Thu, Sep 27, 2007 at 07:45:58PM -0300, Daniel Gorín wrote:
After replacing them with case statements everything compiles fine.... as long as I don't turn on -O2 optimizations :(
This boiled-down example illustrates my problem:
Thanks for the testcase! I've trac'ed it here: http://hackage.haskell.org/trac/ghc/ticket/1746 Thanks Ian
participants (3)
-
Daniel Gorín -
Ian Lynagh -
Simon Peyton-Jones