On Tue, Sep 02, 2008 at 10:10:31AM +0100, Sittampalam, Ganesh wrote:
Contrived example follows:
module Module1 (mod1) where import Module2
glob1 :: IORef Int glob1 <- mod2 >>= newIORef
mod1 :: IO Int mod1 = readIORef glob1
module Module2 (mod2) where
import Module1
glob2 :: IORef Int glob2 <- mod1 >>= newIORef
mod2 :: IO Int mod2 = readIORef glob2
This is illegal because you're only allowed to use ACIO in top level <- bindings and readIORef isn't (and clearly could not be) ACIO.
(made a couple of changes to quoted example; added import statements and explicit export lists)
Even though I never call writeIORef on glob1 or glob2, and can change the example as above so we don't export them, so it's impossible to ever do so?
As an alternative, consider
module Module1 (mod1) where import Module2
glob1 :: Int glob1 <- return $! mod2
mod1 :: Int mod1 = glob1
module Module2 (mod2) where
import Module1
glob2 :: Int glob2 <- return $! mod1
mod2 :: Int mod2 = glob2
Even more artificial, of course.
Arguably both of these cases are not ACIO simply because of the non-termination effects, but it's not obvious to me how you tell just by looking at either one's code together with the declared API of the other. Is anything strict automatically forbidden by ACIO?
Isn't this just a pure infinite loop? Why is it a problem that ACIO allows you the flexibility that's present in any pure code? David