'ack.bas
DECLARE FUNCTION ack! (m!, n!)
i = 3: j = 2
PRINT "ack("; i; ","; j; ") = "; ack(i, j)
END

FUNCTION ack (m, n)
  IF m < 0 OR n < 0 THEN       'm<0 or n<0
    temp = 0
  ELSEIF m = 0 THEN            'm=0 and n>=0
    temp = n + 1
  ELSEIF n = 0 THEN            'm>0 and n=0
    temp = ack(m - 1, 1)
  ELSE                         'm>0 and n>0
    temp = ack(m - 1, ack(m, n - 1))
  END IF
  ack = temp
END FUNCTION

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