The getter and setter abstractions are really more universal concept than Attr in GIO and StateVariable in HOpenGL. The get and set functions are not limited to IO monad and can be implemented for many others monad types. Unfortunately proper implementation requires functional dependencies. The attached module contains definitions for get and set functions for IO, ST, Reader, ReaderT, State, StateT, RWS and RWST monads. The idea is that each monad can maintains some kind of state and the corresponding Attr type gives access to some part of the state. The good example is the StateAttr with State monad. Example: data Point = Point {x :: Int, y :: Int} attrX :: StateAttr Point Int attrX = StateAttr x (\v p -> p{x=v}) attrY :: StateAttr Point Int attrY = StateAttr y (\v p -> p{y=v}) move :: Int -> Int -> State Point Int move vx vy = do x <- get attrX attrX =: x+vx y <- get attrY attrY =: y+vy I propose to standardize this concept and add Attr module to the GHC base package. Cheers, Krasimir __________________________________________________ Do you Yahoo!? Yahoo! Shopping - Send Flowers for Valentine's Day http://shopping.yahoo.com