Corrected HasUpdate's superclass constraint, fixes #4.

Author: svenpanne

LICENSE

@@ -1,5 +1,5 @@
 Copyright (c) 2014-2015, Edward Kmett
-Copyright (c) 2009-2014, Sven Panne
+Copyright (c) 2009-2016, Sven Panne
 All rights reserved.
 
 Redistribution and use in source and binary forms, with or without

StateVar.cabal

@@ -1,12 +1,12 @@
 name: StateVar
-version: 1.1.0.3
+version: 1.1.0.4
 synopsis: State variables
 description:
   This package contains state variables, which are references in the IO monad,
   like IORefs or parts of the OpenGL state.
 homepage: https://github.com/haskell-opengl/StateVar
 bug-reports: https://github.com/haskell-opengl/StateVar/issues
-copyright: Copyright (C) 2014-2015 Edward A. Kmett, 2009-2015 Sven Panne
+copyright: Copyright (C) 2014-2015 Edward A. Kmett, 2009-2016 Sven Panne
 license: BSD3
 license-file: LICENSE
 author: Sven Panne and Edward Kmett

src/Data/StateVar.hs

@@ -10,7 +10,7 @@
 --------------------------------------------------------------------------------
 -- |
 -- Module      :  Data.StateVar
--- Copyright   :  (c) Edward Kmett 2014-2015, Sven Panne 2009-2014
+-- Copyright   :  (c) Edward Kmett 2014-2015, Sven Panne 2009-2016
 -- License     :  BSD3
 -- 
 -- Maintainer  :  Sven Panne <[email protected]>
@@ -193,7 +193,7 @@ instance HasSetter (TVar a) a where
 infixr 2 $~, $~!
 
 -- | This is the class of all updatable state variables.
-class HasSetter t a => HasUpdate t a b | t -> a b where
+class HasSetter t b => HasUpdate t a b | t -> a b where
   -- | Transform the contents of a state variable with a given funtion.
   ($~) :: MonadIO m => t -> (a -> b) -> m ()
 #if USE_DEFAULT_SIGNATURES