ghc: panic! (the 'impossible' happened)

[aSect]

i tried to load the following code in ghci:

{-# OPTIONS_GHC -Wall -O2 #-}

module Main where

import Data.Map (Map) import qualified Data.Map as Map

data Vertex a

= Vertex { vname :: a } deriving (Show, Read, Eq)

data Edge a

= Edge { xedge :: a

, yedge

a } deriving (Show, Read, Eq)

data Graph a

= Graph { vertexes :: [Vertex a]

, edges

[Edge a]

, adjacents

Vertex a -> [Vertex a] } deriving (show, Read, Eq)

and then i got the following error:

ghc: panic! (the 'impossible' happened)

(GHC version 7.4.1 for x86_64-unknown-linux):

nameModule show{tv a25N}

[guest]

It was fixed by #5961.