1 point by cchooper 3324 days ago | link The problem is: what's a concise way of expressing the new order? Perhaps something like this:`````` ((reorder foo (x y z) (z x y)) 1 2 3) `````` but it's so clunky it's not really worth it. If you could reflect on functions to see their parameter list, then you could do this:`````` (def foo (x y z) ...stuff...) ((reorder foo (z x y)) 1 2 3) `````` A little better.-----
 1 point by cchooper 3323 days ago | link Ah yes, cycle notation!`````` ; convert a cycle into transpositions (def trans (cycle (o first nil)) (if (no cycle) nil (~cdr cycle) (list:list cycle.0 first) (cons (list cycle.0 cycle.1) (trans (cdr cycle) (if first first cycle.0))))) ; permute a list using a list of disjoint cycles (def permute (cycles l) (with (ts (apply join (map trans cycles)) ret (copy l)) (map [= (ret (- _.1 1)) (l (- _.0 1))] ts) ret)) (permute '((1 2 3) (4 5)) '(a b c d e)) => (c a b e d)``````-----
 2 points by shader 3323 days ago | link hmm. I think that cycle notation is sometimes shorter than just stating the final positions, but only rarely.How about a function that does:`````` >(reorder '(2 5 4 1 3) '(a b c d e)) '(b e d a c) `````` That makes more sense in many cases. But having a function that does permutations using cycle notation is probably also useful.-----