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2 points by Pauan 3109 days ago | link | parent

"So I suppose it would not do to just expand it into ((compose orig-cc fn) ...), and we have to actually make it a real function composition."

Not so. If you look at line 29 in ac.scm you'll see this:

  ; the next three clauses could be removed without changing semantics
  ; ... except that they work for macros (so prob should do this for
  ; every elt of s, not just the car)
  ((eq? (xcar (xcar s)) 'compose) (ac (decompose (cdar s) (cdr s)) env))
  ((eq? (xcar (xcar s)) 'complement)
   (ac (list 'no (cons (cadar s) (cdr s))) env))
  ((eq? (xcar (xcar s)) 'andf) (ac-andf s env))
For those not familiar with the Arc compiler, what it's doing is basically these transformations:

  ((compose foo bar) 1) -> (foo (bar 1))

  ((complement foo) 1)  -> (no (foo 1))

  ((andf foo bar) 1)    -> (let g1 1 (and (foo g1) (bar g1)))
If you wish for compose, complement, and andf to work on macros and special forms like fn, your compiler will need to do a similar transformation. The catch is that this transformation only works in functional position:

  (map no:do (list 1 2 3 nil nil)) ;; doesn't work
It's all very hacky and whatnot, macros aren't very clean at all in Arc. The other catch is that it hardcodes the symbols 'compose, 'complement, and 'andf, but my Nu compiler fixes that.

3 points by dido 3109 days ago | link

I figured that out and my compiler now does that transformation for compose in:

Will see if we can't apply the same for complement and andf in the same way. :)