Quicksort in Hoon!

qsort.hoon

|=  l=(list @ud)
^-  (list @ud)
?:  =(0 (lent l))
  ~
=/  pivot  (snag 0 l)
=/  rest  (slag 1 l)
=/  less  (skim rest |=(a=@ (lte a pivot)))
=/  more  (skim rest |=(a=@ (gth a pivot)))
:(weld $(l less) ~[pivot] $(l more))

Quick (ha) reference implementation I wrote in Python of how the Hoon code "should" work:

def qsort(l):
    if len(l) == 0: return []
    pivot = l[0]
    less = qsort([i for i in l[1:] if i <= pivot])
    more = qsort([i for i in l[1:] if i > pivot])
    return less + [pivot] + more