Hello zaxis, Thursday, October 22, 2009, 11:28:14 AM, you wrote:
> aaa <- newIORef ([]::[(Int,Int)]) > writeIORef aaa [(1,1),(2,2),(3,3)] > then if i want to change aaa to [(1,1),(2,222),(3,3)] , what's the best way > ? > re-write aaa is not permitted. it's the only way. in Haskell, you have *immutable* values. aaa is a reference to immutable value. you can mutate reference so it will point to another immutable value but you cannot change this value. there are two ways to make aaa==[(1,1),(2,222),(3,3)]. first, you can apply function to whole value: value <- readIORef aaa writeIORef aaa (f value) second, you may create list of IORefs, tuple of IORefs and so: a <- newIORef (1,1) ... let aaa = [a,b,c] now aaa is a immutable list of mutable IORefs. of course, you can create IORef pointing to list of IORefs too -- Best regards, Bulat mailto:bulat.zigans...@gmail.com _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
