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Test case:

{-# LANGUAGE TemplateHaskell #-}
import Language.Haskell.TH

_ = $(newName "x" >>= varE)

Result:

$ runghc test.hs 
ghc: panic! (the 'impossible' happened)
  (GHC version 7.4.1 for x86_64-unknown-linux):
	nameModule x_aSd{v}

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

Similar results from ghci:

$ ghci
GHCi, version 7.4.1: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Prelude> :set -XTemplateHaskell
Prelude> import Language.Haskell.TH
Prelude Language.Haskell.TH> $(newName "x" >>= varE)
Loading package array-0.4.0.0 ... linking ... done.
Loading package deepseq-1.3.0.0 ... linking ... done.
Loading package containers-0.4.2.1 ... linking ... done.
Loading package pretty-1.1.1.0 ... linking ... done.
Loading package template-haskell ... linking ... done.
ghc: panic! (the 'impossible' happened)
  (GHC version 7.4.1 for x86_64-unknown-linux):
	nameModule x_aSm{v}

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

Note that referencing an undefined name via mkName generates a reasonable error message rather than "the impossible happened":

Prelude Language.Haskell.TH> $(varE $ mkName "x")

<interactive>:6:3:
    Not in scope: `x'
    In the result of the splice:
      $(varE $ mkName "x")
    To see what the splice expanded to, use -ddump-splices
    In the expression: $(varE $ mkName "x")
    In an equation for `it': it = $(varE $ mkName "x")

Trac metadata

Trac field	Value
Version	7.4.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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