SML - How to create a list out of a postorder scan of a tree -

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how implement function in sml gets tree , returns list. list consists of values in tree nodes according postorder scan of tree.

the tree datatype is:

datatype 'a tree = leaf | branch of 'a * 'a tree * 'a tree;

that can done by:

 fun createlist(leaf) = [] =   | createlist(branch(el, left, right)) = createlist(left) @ createlist(right) @ [el];

if have branch first visit it's left subtree (createlist(left)), it's right subtree (createlist(right)) , afterwards append element el, postorder tree traversal does. if want create list leaf (an empty tree) result empty list.


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