Merge sort in Hoon

merge.hoon

|%
++  merge
  |=  [a=(list @) b=(list @)]
  ^-  (list @)
  =|  c=(list @)
  |-
  =/  empty-a  =(0 (lent a))
  =/  empty-b  =(0 (lent b))
  ?:  ?|(empty-a empty-b)
    :(weld c a b)
  =/  first-a  (snag 0 a)
  =/  first-b  (snag 0 b)
  ?:  (lth first-a first-b)
    $(c (snoc c first-a), a (slag 1 a))
  $(c (snoc c first-b), b (slag 1 b))
++  sort
  |=  l=(list @)
  ?:  =(1 (lent l))
    l
  =/  middle  (div (lent l) 2)
  =/  left   $(l (scag middle l))
  =/  right  $(l (slag middle l))
  (merge left right)
--