#6114: ghc: panic! occurred with use of isInstance, newName and a type splice
--------------------------------+-------------------------------------------
Reporter: davidmiani | Owner:
Type: bug | Status: new
Priority: normal | Component: Template Haskell
Version: 7.4.1 | Keywords:
Os: MacOS X | Architecture: x86_64 (amd64)
Failure: Compile-time crash | Testcase:
Blockedby: | Blocking:
Related: |
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Compiling the below code:
{{{
{-# LANGUAGE TemplateHaskell #-}
module Test where
import Language.Haskell.TH
import Control.Monad.Instances ()
instanceVar = $(do
xName <- newName "x"
instanceType <- [t| (Int -> $(varT xName)) |]
instanceOfFunctor <- isInstance ''Functor [instanceType]
stringE $ show instanceOfFunctor
)
}}}
Results in the following error:
{{{
[1 of 1] Compiling Test ( test.hs, interpreted )
test.hs:6:17:
Exception when trying to run compile-time code:
ghc: panic! (the 'impossible' happened)
(GHC version 7.4.1 for x86_64-apple-darwin):
nameModule x_a1ws{tv}
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
Code: do { xName <- newName "x";
instanceType <- [t| Int -> $(varT xName) |]
pending [(splice, varT xName)];
instanceOfFunctor <- isInstance ''Functor [instanceType];
.... }
In the expression:
$(do { xName <- newName "x";
instanceType <- [t| Int -> $(varT xName) |];
instanceOfFunctor <- isInstance ''Functor [instanceType];
.... })
In an equation for `instanceVar':
instanceVar
= $(do { xName <- newName "x";
instanceType <- [t| Int -> $(varT xName) |];
.... })
Failed, modules loaded: none.
}}}
While the code is not correct (replacing the `instanceType` line with
`instanceType <- [t| (->) Int |]`
fixes the problem), a better error message would be desirable.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6114>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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