# iterative program to sum elements of an array

# store in a file such as "sum.mpd"
# compile by executing "mpd sum.mpd"
# run by executing "a.out size"
#
# Version "rekursives Doppeln", Jost Berthold
#  (Original aus mpd-Tutorial)
##############################################

resource sum()

  # forward-Deklaration von sumR für die Rekursion
  op sumR(int a[1:*]) returns int;


  # declare and read first command-line argument
  int size; getarg(1,size);

  # declare and initialize array a
  int a[1:size];         # same as int a[size]
  for [i = 1 to size] {
    a[i] = i;
  }

  # Aufruf der Rekursion:
  int total
  total = sumR(a)

  write("the sum of 1 ...", size, "is", total);

  # Rekursive Prozedur sumR
  proc sumR(a) returns sum {
    int laenge
    laenge = ub(a)

    if (laenge == 1) { sum=a[1]; }
     else {
	 real halb; int teilen
	 halb =  ceil( log(laenge,2) ) - 1
         teilen = int(2**(halb))

	 int i,links,rechts

	 for[i = 0 to 1] {
	      links = sumR(a[1:teilen])
 	      rechts= sumR(a[teilen+1 : laenge])
	}

	 sum = links + rechts
     }   
    # return sum, implizit
  }

end