;;;;;
;;;;;
;;;;; Sum of Cubes
;;;;;
;;;;;

; Infintite list of sum of cubes.
; -- [m n (+ m^3 n^3)]
(define $sum-of-cubes
  (let {[$cube (lambda [$x] (* x (* x x)))]}
    (match-all nats (list integer)
      [<join _ (& <cons $m _> <join _ <cons $n _>>)> [m n (+ (cube m) (cube n))]])))

; sample output
(test (take 10 sum-of-cubes))

; list numbers that is the sum of two non-zero cube numbers
(test (take 2 (match-all sum-of-cubes (list [integer integer integer])
                [<join _ <cons [$x1 $y1 $c]
                  <join _ <cons [$x2 $y2 ,c]
                   _>>>>
                 [[x1 y1 c] [x2 y2 c]]]
                )))