Simon Marlow wrote: > > > > I don't know how to achieve the same goal with > > > atomicModifyIORef. > > > > I do. To modify ioRef1 and ioRef2 "simultaneously", write > > > > atomicModifyIORef ioRef1 (\ contents1 -> unsafePerformIO > > ioRef2 (\ contents2 -> blah blah)) > > > > The actual modification will take place when the result or > > contents of ioRef1 or ioRef2 get evaluated. > > I don't understand how this works. Unless I'm missing something, you'll > see the contents of ioRef1 at the point at which the first > atomicModifyIORef takes place, but the contents of ioRef2 from the time > at which the unsafePerformIO is evaluated, which is some unspecified > time later.
Perhaps we're talking about different sorts of atomicModifyIORef? I am now thinking of atomicModifyIORef as having the type IORef a -> (a -> (a,b)) -> IO b Thus when it is called the effect is to construct (1) a thunk of type (a,b) containing the application of the function to the thunk previously in the IORef; (2) a thunk containing fst $ the thunk from (1) of type (a,b), which is put in the IORef; (3) a thunk containing snd $ the thunk from (1), to be returned. Subsequent evaluation of the result of atomicModifyIORef will force the thunks in (1) and (3) to be evaluated, meaning the unsafePerformIO gets evaluated. _______________________________________________ FFI mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/ffi
