[GHC] #1809: type families: difference in type-checking between compile-time and run-time

[GHC]

#1809: type families: difference in type-checking between compile-time and run-
time
-------------------------+--------------------------------------------------
    Reporter:  guest     |        Owner:         
        Type:  bug       |       Status:  new    
    Priority:  normal    |    Milestone:         
   Component:  Compiler  |      Version:  6.8    
    Severity:  normal    |   Resolution:         
    Keywords:            |   Difficulty:  Unknown
          Os:  Linux     |     Testcase:         
Architecture:  x86       |  
-------------------------+--------------------------------------------------
Comment (by guest):

 simpler program showing same effect:

 {{{
 {-# LANGUAGE TypeFamilies #-}

 module Main where

 import Prelude hiding (head)
 import qualified Prelude

 type family Elem a :: *

 type instance Elem [a] = a

 head :: [a] -> Elem [a]
 head = Prelude.head

 x = head [1 :: Int,2,3]

 main = putStrLn . show $ x
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1809#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler