Re: [Caml-list] Type problem... possible design problem

[Richard Jones <rich@annexia.org>]

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On Sat, Dec 18, 2004 at 02:28:09PM +0000, chris.danx wrote:
> My concern with variants is sharing subgraphs in graphs, will they be 
> shared or copied?

A tree structure like this should be stored shared:

  type 'a tree = Leaf of 'a | Node of 'a tree list

You can prove this; for instance:

# let n = ref 1;;
val n : int ref = {contents = 1}
# let t = Leaf n;;  
val t : int ref tree = Leaf {contents = 1}
# let tree = Node [t; t];;
val tree : int ref tree = Node [Leaf {contents = 1}; Leaf {contents = 1}]
# n := 2;;
- : unit = ()
# tree;;
- : int ref tree = Node [Leaf {contents = 2}; Leaf {contents = 2}]

Rich.

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