ghc: panic! (the 'impossible' happened)

Error when compiling, maybe parser wasn't able to detect error at "type TokContent = { position :: Pos, content::String }"

ghc: panic! (the 'impossible' happened)

(GHC version 7.6.3 for x86_64-unknown-linux):

tc_hs_type: record

{-# LANGUAGE DeriveDataTypeable #-}

module Tokens(
    Token     (..),
    Pos
) where

import Data.Data(toConstr,Data,Typeable)

type Pos = (Int,Int)
type TokContent = { position :: Pos, content::String }

data Token =  TkString    { position :: Pos, content::String }
            | TkLB        { position :: Pos, content::String }
            | TkRB        { position :: Pos, content::String }
            | TkLCurly    { position :: Pos, content::String }
            | TkRCurly    { position :: Pos, content::String }
            | TkLP        { position :: Pos, content::String }
            | TkRP        { position :: Pos, content::String }
            | TkDColon    { position :: Pos, content::String }
            | TkColon     { position :: Pos, content::String }
            | TkSColon    { position :: Pos, content::String }
            | TkTEQ       { position :: Pos, content::String }
            | TkPEQ       { position :: Pos, content::String }
            | TkDot       { position :: Pos, content::String }
            | TkExcMark   { position :: Pos, content::String }
            | TkNEQ       { position :: Pos, content::String }
            | TkDAmp      { position :: Pos, content::String }
            | TkAnd       { position :: Pos, content::String }
            | TkPOr       { position :: Pos, content::String }
            | TkOr        { position :: Pos, content::String }
            | TkDEQ       { position :: Pos, content::String }
            | TkGE        { position :: Pos, content::String }
            | TkLE        { position :: Pos, content::String }
            | TkGT        { position :: Pos, content::String }
            | TkLT        { position :: Pos, content::String }
            | TkIDiv      { position :: Pos, content::String }
            | TkDiv       { position :: Pos, content::String }
            | TkSum       { position :: Pos, content::String }
            | TkMin       { position :: Pos, content::String }
            | TkPower     { position :: Pos, content::String }
            | TkTimes     { position :: Pos, content::String }
            | TkMod       { position :: Pos, content::String }
            | TkEq        { position :: Pos, content::String }
            | TkAssign    { position :: Pos, content::String }
            | TkInt       { position :: Pos, content::String }
            | TkBool      { position :: Pos, content::String }
            | TkChar      { position :: Pos, content::String }
            | TkVoid      { position :: Pos, content::String }
            | TkFloat     { position :: Pos, content::String }
            | TkStruct    { position :: Pos, content::String }
            | TkUnion     { position :: Pos, content::String }
            | TkEnum      { position :: Pos, content::String }
            | TkEnumCons  { position :: Pos, content::String }
            | TkNull      { position :: Pos, content::String }
            | TKGlobal    { position :: Pos, content::String }
            | TkFunc      { position :: Pos, content::String }
            | TkIf        { position :: Pos, content::String }
            | TkElif      { position :: Pos, content::String }
            | TkElse      { position :: Pos, content::String }
            | TkEnd       { position :: Pos, content::String }
            | TkWhile     { position :: Pos, content::String }
            | TkFor       { position :: Pos, content::String }
            | TkBegin     { position :: Pos, content::String }
            | TkBreak     { position :: Pos, content::String }
            | TkContinue  { position :: Pos, content::String }
            | TkReturn    { position :: Pos, content::String }
            | TkExit      { position :: Pos, content::String }
            | TkRead      { position :: Pos, content::String }
            | TkWrite     { position :: Pos, content::String }
            | TkPrint     { position :: Pos, content::String }
            | TkAlloc     { position :: Pos, content::String }
            | TkFree      { position :: Pos, content::String }
            | TkSizeOf    { position :: Pos, content::String }
            | TkGet       { position :: Pos, content::String }
            | TkTruFal    { position :: Pos, content::String }
            | TkNum       { position :: Pos, content::Int   }
            | TkDId       { position :: Pos, content::String }
            | TkId        { position :: Pos, content::String }
            | TkError     { position :: Pos, content::String }
            deriving(Data,Typeable)

instance Show Token where
  show generic = show (toConstr generic )++ "\n" ++
                 "    line:   " ++ show l ++ "\n" ++
                 "    column: " ++ show c ++ "\n"
                where (l,c) = position generic

Trac metadata

Trac field	Value
Version	7.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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Architecture