[Haskell-cafe] Top Level <-

[Adrian Hey]

Sittampalam, Ganesh wrote:
> Can't you write two recursive modules with <- that depend on
> each other, so that there's no valid initialisation order?
> 
> Contrived example follows:
> 
> module Module1 where
> 
> glob1 :: IORef Int
> glob1 <- mod2 >>= newIORef 
> 
> mod1 :: IO Int
> mod1 = readIORef glob1
> 
> module Module2 where
> 
> glob2 :: IORef Int
> glob2 <- mod1 >>= newIORef 
> 
> mod2 :: IO Int
> mod2 = readIORef glob2

Immediatly breaking my promise to shut up..

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.

Regards
--
Adrian Hey