#5287: The 'impossible' happened. solveDerivEqns: probable loop
-------------------------------+--------------------------------------------
Reporter: agocorona | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.0.3
Keywords: solveDerivEqns | Testcase:
Blockedby: | Difficulty:
Os: Windows | Blocking:
Architecture: x86 | Failure: Compile-time crash
-------------------------------+--------------------------------------------
Description changed by igloo:
Old description:
> This code:
>
> --------- begin of code------
>
> {-# LANGUAGE FlexibleInstances, UndecidableInstances
> , MultiParamTypeClasses
> #-}
>
> class Serializable a b
>
> class IResource a --The rest of the instance definitions does not
> matter for the error
>
> instance Serializable a b => IResource a
>
> data DBRef a= DBRef String a
>
> instance (IResource a) => Read (DBRef a)
>
> data Votation a= Votation{
> content :: DBRef a
> } deriving (Read)
>
>
> ------------------------------- end of code ---
>
> gives the following error at compilation time:
>
> tests>runghc impossiblelloop.hs
> ghc: panic! (the 'impossible' happened)
> (GHC version 7.0.3 for i386-unknown-mingw32):
> solveDerivEqns: probable loop
> (impossiblelloop.hs:20:13-16 main:Main.$fReadVotation{v rhI} [a{tv
> abB} [tv]
> ] base:GHC.Read.Read{tc 2d} [main:Main.Votation{tc rbo}
>
> a{tv abB} [tv]] = [base:GHC.Read.Read{tc
> 2d}
>
> (main:Main.DBRef{tc
> rbu}
>
> a{tv abB} [tv])])
> [[main:Main.Serializable{tc rbA} a{tv abB} [tv] b{tv ajE} [tcs]]]
>
> Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
New description:
This code:
{{{
{-# LANGUAGE FlexibleInstances, UndecidableInstances
, MultiParamTypeClasses
#-}
class Serializable a b
class IResource a --The rest of the instance definitions does not
matter for the error
instance Serializable a b => IResource a
data DBRef a= DBRef String a
instance (IResource a) => Read (DBRef a)
data Votation a= Votation{
content :: DBRef a
} deriving (Read)
}}}
gives the following error at compilation time:
{{{
tests>runghc impossiblelloop.hs
ghc: panic! (the 'impossible' happened)
(GHC version 7.0.3 for i386-unknown-mingw32):
solveDerivEqns: probable loop
(impossiblelloop.hs:20:13-16 main:Main.$fReadVotation{v rhI} [a{tv
abB} [tv]
] base:GHC.Read.Read{tc 2d} [main:Main.Votation{tc rbo}
a{tv abB} [tv]] = [base:GHC.Read.Read{tc
2d}
(main:Main.DBRef{tc
rbu}
a{tv abB} [tv])])
[[main:Main.Serializable{tc rbA} a{tv abB} [tv] b{tv ajE} [tcs]]]
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
}}}
--
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5287#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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