I think you're looking for IORef http://www.haskell.org/ghc/docs/
latest/html/libraries/base/Data-IORef.html
Something like this (untested) should do what you want:
example :: IO ()
example = do { ref <- newIORef 1000; loop ref }
where loop ref = do
x <- readIORef ref
print x
when (x>1) (writeIORef ref (x/2) >> loop ref)
On Feb 2, 2006, at 10:57 AM, Maurício wrote:
Donald Bruce Stewart wrote:
briqueabraque:
Hi,
I would like to know what options I have in Haskell to do
something similar to this C++ code:
double a = 1000;
while (a>1) a/=2;
I'm able to do that with lists, but I would like to know how to
do that with monads and variables with state.
You'll get good code using a normal recusive loop:
main = print (loop 1000)
where
loop a | a <= 1 = a | otherwise
= loop (a/2)
All such control structures may be implemented using recursion.
-- Don
I understand those examples, but I really would like to know how
to do that with monads. I would like to ask the same question, but
now with this code:
double a = 1000;
double b = 0;
while (a != b) {
a /= 2;
cout << a; // Prints a
cin << b; // User gives a number, stored in b
};
Best,
Maurício
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