Re: [Haskell-cafe] trees and pointers

15 Jul 2010

      2010/7/15 Serguey Zefirov :
...
2010/7/14 Sergey Mironov :
...
Hi cafe! I have a question of C-to-Haskell type:)
Imagine web application wich allows users to browse some shared
filesystem located at the server.
Application stores every users's position within that filesystem
(current directory or file).
In C this can be implemented with the help of following data types:
Any ideas?
Use IORef. ;)
PS
MVar is better, actually.
Somehow I forgot about them:) Code will turn into something like

data TreeNodeData = File | Dir (IORef TreeNode)
data TreeNode = TreeNode {
        next :: Maybe (IORef TreeNode),
        prev :: Maybe (IORef TreeNode),
        up :: Maybe (IORef TreeNode), -- missed it in original C example
        payload :: TreeNodeData
	}

data User = User {
	position :: IORef TreeNode,
	-- ...
	}

It really should work! (we don't take multithreading issues into
account for now)
Slightly annoying thing is that 1-to-1 mapping from C to Haskell also
forces programmer to perform C-like low-level pointer linking.

-- 
Thanks,
Sergey