On 08/04/2013 02:50 AM, Meta wrote:
On Saturday, 3 August 2013 at 23:04:14 UTC, Timon Gehr wrote:
...
Modification and dereference within a Haskell expression:
import Data.STRef
import Control.Monad.ST
x = runST $ do
x <- newSTRef 0
writeSTRef x 1
v <- readSTRef x
return v
main = print x
I apologize, as I don't know how familiar you are with Haskell,
With the language, quite intimately.
so forgive me if I'm telling you something you already know. That code is
100% pure and side-effect free;
My point was basically that x is a pure expression of type Integer.
no variables are being modified.
Which I didn't claim. A reference is dereferenced and the contents of
the referenced slot are replaced. Then the reference is dereferenced
again to read the modified value out.
Haskell only simulates side-effects
What tells you that D does not 'simulate' mutable state?
with monads,
What is done to main behind the scenes in order to execute the program
is most definitely side-effecting.
and do-notation
do notation is not central to my point.
(syntwhat you
use in this example) which is syntactic sugar.
(i.e., the academic definition of purity).
I wouldn't go that far.
Perhaps that may go too far, as academics love to obfuscate topics with
a bunch of extraneous cruft,
I take issue with this statement. I meant, I wouldn't assume 'the
academic definition of purity' is a thing.
but the fact remains that purity means:
1. No modification of local or global state (side-effects)
2. No dependence on global mutable state.
What does this statement quantify over? Eg, where is the abstraction
boundary?
