lolcathost% ghci
GHCi, version 7.10.3: http://www.haskell.org/ghc/  :? for help
> import Data.IORef
import Data.IORef
> x <- newIORef 5
> let f y = (+) <$> readIORef x <*> pure y
> f 10
15
> writeIORef x 0
> f 10
10
>
Leaving GHCi.
lolcathost% poly
Poly/ML 5.6 Release
> val x = ref 5;
val x = ref 5: int ref
> fun f y = !x + y;
val f = fn: int -> int
> f 10;
val it = 15: int
> x := 0;
val it = (): unit
> f 10;
val it = 10: int
lolcathost%