On Tue, Sep 28, 2010 at 8:54 AM, Felipe Lessa <felipe.le...@gmail.com> wrote: > On Tue, Sep 28, 2010 at 10:41 AM, Peter Robinson <thaldy...@gmail.com> wrote: >> readTVarIO :: TVar a -> IO a > > One needs to know if it is ok to wrap this IO action into an STM > action. For example, > >> data I a = I a >> >> looselyReadTVar :: TVar a -> STM a >> looselyReadTVar tvar = >> let v = unsafePerformIO (I <$> readTVarIO tvar) >> in case v of I x -> return x > > The 'case' is needed because otherwise the TVar would be read > only when its value was requested, and we want to keep the > ordering. The 'I' datatype is used to avoid evaluating the > user's value (which could even be 'undefined'). > > Note that this function can be used on any monad, but I don't > think that is a good idea =). > > Cheers! >
Isn't there an 'unsafeIOToSTM' function somewhere? Something like: > unsafeIOToSTM (IO k) = STM k Then you might not need the case statement. Antoine _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
