#7438: Tc panic when type declaration is missing
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Reporter: heisenbug | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 7.7 | Keywords:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: GHCi crash | Blockedby:
Blocking: | Related:
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Compile the attached snippet with HEAD GHC.
> ghc: panic! (the 'impossible' happened)
> (GHC version 7.7.20121114 for x86_64-unknown-linux):
> tcTyVarDetails
> <<details unavailable>>
You need to install the "thrist-0.3" package from Hackage.
When I just paste the 'Thrist' definition into the code the panic does not
happen. (It resulted in this message for me:
> Occurs check: cannot construct the infinite type: t2 ~ 'St t2
> Expected type: Thrist Nat (At t4) t2 t3
> Actual type: Thrist Nat (At t4) b t3
> Relevant bindings include
> go :: Thrist Nat (At t4) t2 t3 -> t -> t1
> (bound at GHC-7438.hs:20:11)
> In the first argument of `go', namely `rest'
> In the second argument of `(:)', namely `go rest acc'
> In the expression: c : go rest acc
> Failed, modules loaded: none.
)
Looks like interaction of non-generalized (local) let in conjunction with
imported polykinded GADT.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7438>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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