Personally I would use binary trees. One could also define a datatype like this one:
datatype 'a nestl = A of 'a * 'a nestl | B of 'a nestl list * 'a nestl | NIL;
datatype 'a nestl = A of 'a * 'a nestl | B of 'a nestl list * 'a nestl | NIL
A (3, B ([A(2,NIL)], A(4, A (5, NIL))));
val it = A (3, B ([A (2, NIL)], A (4, A (5, NIL)))): int nestl
That's not very elegant though.
Larry Paulson
On 11 Oct 2016, at 15:28, David Topham <dtopham at ohlone.edu> wrote:
I doubt if I am the first person to ask this question, but I have not seen an "answer" in any of the ML books I have read yet...
Is there a way to represent a "set of sets" so that a function can process a query such as " is [2] an element of [ 3 , [2], 4, 5]?"
I know we can easily do a query such as " is 2 an element of [ 3 , 2, 4, 5]?"
I know the problem is that lists cannot have different types, but this is a common, normal query in mathematics so someone must have figured out a way to do it perhaps?
-Dave
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