On Sun, Sep 9, 2012 at 1:46 AM, Milan Straka
Hi all,
is there any way to perform a destructive update on a plain ADT? Imagine I have a simple data Tree a = Nil | Node a (Tree a) (Tree a) I would like to be able to modify right subtree of an existing tree.
I can do that for example when using IORefs by changing the datatype to data Tree a = Nil | Node a (IORef (Tree a)) (IORef (Tree a)) and use unsafePerformIO + writeIORef. But the IORefs cause additional complexity when working with the data type.
At the moment I am interested in any GHC solution, be it non-portable or version specific. I would like just to run some benchmarks and see the results.
Cheers, Milan
You can do it if you refer to the children using Array#s. That's what I do in unordered-containers to implement a more efficient fromList. For arbitrary field types I don't think there's a way (although it would be useful when birthing persistent data structures). -- Johan