Am Sonntag 21 Februar 2010 16:30:00 schrieb Vojtěch Knyttl:
Hello,
I am trying to create STArray with newListArray like this: la x y = newListArray ((1,1),(x,y)) [(x'+y') | x' <- [1..x], y' <- [1..y]]
– but it does not work: No instance for (MArray a Field m)
I tried to define the type like this, but it would not work either: la :: Int -> Int -> STArray (Int,Int) Field
STArrays have a "state parameter", newListArray ((1,1),(x,y)) [(x'+y') | x' <- [1 .. x], y' <- [1 .. y]] has type forall s. ST s (STArray s (Int,Int) Int) So la :: forall s. Int -> Int -> ST s (STArray s (Int,Int) Int) la x y = newListArray ((1,1),(x,y)) [(x'+y') | x' <- [1 .. x], y' <- [1 .. y]] You can use STArrays only in the ST monad, there you'd do something like runST (do arr <- la 23 25 use arr return result)
It is obvious that I don't get the syntax of using it, so I will appreciate any suggestions.
V. K.