Iteration and Recursion in Hoon.

Code below is a part of Exercise: A Playing Card Library ¹ section in Hoon School 7. Libraries.

++  shuffle-deck
  |=  [unshuffled=deck entropy=@]
  ^-  deck
  =/  shuffled  *deck
  =/  random  ~(. og entropy)
  =/  remaining  (lent unshuffled)
  |-
  ?:  =(remaining 1)
    :_  shuffled
    (snag 0 unshuffled)
  =^  index  random  (rads:random remaining)
  %=  $
    shuffled      [(snag index unshuffled) shuffled]
    remaining     (dec remaining)
    unshuffled    (oust [index 1] unshuffled)
  ==

Notice that random card is selected from the following 2 lines.

shuffled      [(snag index unshuffled) shuffled]
unshuffled    (oust [index 1] unshuffled)

unshuffled remove random card. shuffled select the same random card that is removed by unshuffled.

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