#4863: ghc panic when reifying the result of classInstances
-------------------------------+--------------------------------------------
Reporter: guest | Owner:
Type: bug | Status: new
Priority: normal | Component: Template Haskell
Version: 7.0.1 | Keywords:
Testcase: | Blockedby:
Os: Linux | Blocking:
Architecture: x86_64 (amd64) | Failure: Compile-time crash
-------------------------------+--------------------------------------------
{{{
Prelude Language.Haskell.TH Language.Haskell.TH.Syntax> $(fmap show
(classInstances ''Eq [ConT ''Int] >>= reify . head) >>= lift)
<interactive>:1:3:
Exception when trying to run compile-time code:
<interactive>: panic! (the 'impossible' happened)
(GHC version 7.0.1 for x86_64-unknown-linux):
reifyType PredTy
<pred>base:GHC.Classes.Eq{tc 23} ghc-prim:GHC.Types.Int{(w) tc 3J}
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
Code: (>>=)
fmap
(show)
((>>=)
classInstances 'Eq [Language.Haskell.TH.Syntax.ConT
'Int]
(.) reify head)
lift
In the expression:
$(fmap show (classInstances 'Eq [ConT 'Int] >>= reify . head)
>>=
lift)
In an equation for `it':
it
= $(fmap show (classInstances 'Eq [ConT 'Int] >>= reify . head)
>>=
lift)
}}}
The same thing happens when compiling with ghc rather than using GHCi.
Also, it looks like the pretty printer is displaying {{{ ''Eq }}} and {{{
''Int }}} incorrectly.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4863>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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