TCMonad:723 bug

[Sengan.Baring-Gould at nsc.com]

ghci -fglasgow-exts -syslib data x.lhs 
   ___         ___ _
  / _ \ /\  /\/ __(_)
 / /_\// /_/ / /  | |      GHC Interactive, version 5.00.2, For Haskell 98.
/ /_\\/ __  / /___| |      http://www.haskell.org/ghc/
\____/\/ /_/\____/|_|      Type :? for help.

Loading package std ... linking ... done.
Loading package lang ... linking ... done.
Loading package concurrent ... linking ... done.
Loading package posix ... linking ... done.
Loading package util ... linking ... done.
Loading package data ... linking ... done.
Compiling Main             ( x.lhs, interpreted )

x.lhs:5:
    Could not deduce `Ord x' from the context ()
    Probable fix:
        Add `Ord x' to the type signature(s) for {applyElt}
    arising from use of `elt' at x.lhs:5
    In the second argument of `($)', namely `elt fact'
    In the record update: fact {elt = f $ (elt fact)}

x.lhs:5:
    Could not deduce `Ord y' from the context ()
    Probable fix:
        Add `Ord y' to the type signature(s) for {applyElt}
    arising fromghc-5.00.2: panic! (the `impossible' happened, GHC version 5.00.2):
        typecheck/TcMonad.lhs:723: Non-exhaustive patterns in function pp_orig


Please report it as a compiler bug to glasgow-haskell-bugs at haskell.org,
or http://sourceforge.net/projects/ghc/.



Source:

> data (Eq x, Ord x) =>
>      Fact x   = Fact { elt :: x, causes :: [FactID] } deriving (Eq, Ord)

> applyElt        :: (x -> y) -> Fact x -> Fact y
> applyElt f fact  = fact { elt = f $ elt fact }


> main = main
> type FactID = Int



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