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4 points by fallintothis 3351 days ago | link | parent

thinking there must be a function f (like my ssexpandif but more sophisticated)

Not quite. The problem here is not f (entirely), but also treewise.

  (def treewise (f base tree)
    (if (atom tree)
        (base tree)
        (f (treewise f base (car tree)) 
           (treewise f base (cdr tree)))))
treewise will only act on atoms, whereas we need to act on conses sometimes -- namely, quoted items. If we ignore those, it could work:

  (def ssexpand-all (expr)
    (treewise cons
              [let expanded (ssexpand-if expr)
                (if (is _ expanded)
                    _
                    (ssexpand-all expanded))]
              expr))
But ssyntax can expand into more ssyntax; e.g.,

  arc> (ssexpand 'a:.b)
  (compose a .b)
  arc> (ssexpand '.b)
  (get b)
So, we need to recurse in the f argument anyway. At a certain point, it seems like the anonymous & higher-order functions add layers of indirection on what should just be a straightforward recursive definition.

I get really annoyed at that, though, when working with trees in Arc. There always seems to be some underlying pattern that's just different enough that I can't abstract it into a higher-order function.