Decrement written in Hoon

decrement.md

Decrement

Write a gate that takes some integer n and returns (n - 1). You may not use dec from the Hoon stdlib, and you may not look at the code for dec in hoon.hoon. You're under the honor system.

gen-dec-1.hoon

/+  mylib               ::  import
=,  mylib               ::  alias to the subject (don't have to type mylib anymore)
|=  a=@
^-  @
(new-dec a)

mylib.hoon

|%
++  new-dec
  |=  a/@
  ^-  @

  ?:  (lte a 0)                                        ::
    0
    ?:  (lte a 1)
      0
      %-  inner-dec  :+(a 1 0)

++  inner-dec
  |=  e=[a=@ b=[c=@ d=@]]                              :: sample (input mold)
  ^-  @                                                :: return atom

  ::~&  e                                              :: printf
  ?:  (gte c.b.e a.e)                                  :: if (c.b.e >= a.e)
    d.b.e                                              :: yes, return result
    %-  inner-dec  :+(a.e .+(c.b.e) .+(d.b.e))         :: no, call inner-dec with tuple of a.e (c.b.e + 1) and (d.b.e + 1)

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