Saturday, 23 February 2013

Clojure zippers - 2

Continuation of the earlier post on zippers.

So what if you want a tree with content in the parent nodes? Something like this:

We'll have to use records or maps as each node, and then use functions (usually keys) to get the content from the parent. Alex has a blog post on using records, here I'll stick with using a map
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Note that "makenode" simply has to assoc(iate) the provided "children" vector to the existing map to add children.
On a side note, source is an excellent introduction on how to use metadata.

Paths to the root node
Although has the 'path' function that gives the list of nodes traversed from the root to the current node, it contains the whole node rather than just the content of :self. That is easily remedied thus:
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Adding children to all leaf nodes

Adding children to all the leaf nodes is a useful feature in programming a board game, where all the prospective moves are stored in a tree, and we wish to look 4/5/6/n moves ahead. In such cases, we can grow the leaf node (find out the next possible set of moves).

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We use a different function called add-children to create a vector of children to attach to each leaf node

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