TCMonad:723 bug

[Simon Peyton-Jones]

This was a bug in GHC 5.00, fixed in 5.02.

Simon

| -----Original Message-----
| From: Sengan.Baring-Gould at nsc.com 
| [mailto:Sengan.Baring-Gould at nsc.com] 
| Sent: 23 August 2002 23:00
| To: glasgow-haskell-bugs at haskell.org
| Subject: TCMonad:723 bug
| 
| 
| 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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| 
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