Re: Cprod (Cartesian Product) in Lisp (or Scheme)

On Tue, 21 May 2024 12:18:52 -0700
HenHanna <HenHanna@devnull.tb> wrote:

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How would you write this in Lisp (or Scheme) ?
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in Python...    (writing this out: itertools.product([0, 1], repeat=N )
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The value can be a list or a Tuple.
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                  cprod([0, 1], 1) => ((0) (1))
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                  cprod([0, 1], 2) => ((0,0) (0,1) (1,0) (1,1))

 This is cartesian power rather than arbitrary cartesian product. Here
is a Common Lisp version. It only works for vectors.
 (defun cartesian-power
         (vector power
          &aux (len (length vector)) (wheels (make-array power :initial-element 0))
               result (posres 0)
         )
     (when (or (eql power 0) (eql len 0))
         (return-from cartesian-power (make-array 0)))
     (setq result (make-array (expt len power)))
     (do   () (nil)
         (setf (aref result posres)
               (map 'vector (lambda (a) (aref vector a)) wheels))
         (incf posres)
         (let   ((pos (position-if (lambda (a) (< a (1- len))) wheels)))
             (unless pos (return-from cartesian-power result))
             (incf (aref wheels pos))
             (dotimes (i pos) (setf (aref wheels i) 0)))))