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1 point by shader 5678 days ago | link | parent

Nice. Say, that brings up a thought I had earlier.

What if we made that pattern into a function called "maptree". I've needed something like that several times:

  (def maptree (f tree)
    (map (afn (node)
             (if atom.node
                 (f node)
                 (map self node)))
         tree))
It should apply f to each node of the tree, preserving the tree structure. Seems pretty useful to me, if you're going to be doing much transformation of arbitrary list structures.


1 point by shader 5678 days ago | link

In retrospect, it's not much good for transforming the structure, but great for many other things.

For everything else, the other tree functions like trav, treewise, ontree, etc. might be more useful.

How would you make a more general purpose version of maptree that could encompass your transform function? It needs to be able to selectively modify some branches of the tree, and avoid calling map on them. Mine can't do that because it restricts you to atoms. Maybe if it took in two functions, one that operates on atoms, and one on lists, which can then optionally continue the mapping on a subnode. But then what has been gained? You're pretty much writing the whole pattern over again anyway.

Hmm. There seems to be a pattern here, but I can't see how to abstract it out, beyond the somewhat useful but restricted maptree posted above. Ideas?

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