1.1 --- a/src/HOL/Library/Efficient_Nat.thy	Thu May 20 21:19:38 2010 -0700
     1.2 +++ b/src/HOL/Library/Efficient_Nat.thy	Fri May 21 11:50:34 2010 +0200
     1.3 @@ -252,7 +252,7 @@
     1.4  *}
     1.5  
     1.6  code_include Haskell "Nat" {*
     1.7 -newtype Nat = Nat Integer deriving (Show, Eq);
     1.8 +newtype Nat = Nat Integer deriving (Eq, Show, Read);
     1.9  
    1.10  instance Num Nat where {
    1.11    fromInteger k = Nat (if k >= 0 then k else 0);