A-M baby

Task/Forward-difference/REXX/forward-difference-2.rexx

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+/* REXX ***************************************************************
+* Forward differences
+* 18.08.2012 Walter Pachl derived from PL/I
+**********************************************************************/
+Do n=-1 To 11
+  Call differences '90 47 58 29 22 32 55 5 55 73',n
+  End
+Exit
+
+differences: Procedure
+  Parse Arg a,n
+  m=words(a)
+  Select
+    When n<0 Then Say 'n is negative:' n '<' 0
+    When n>m Then Say 'n is too large:' n '>' m
+    Otherwise Do
+      Do i=1 By 1 while a<>''
+        Parse Var a a.i a
+        End
+      Do i = 1 to n;
+        t = a.i;
+        Do j = i+1 to m;
+          u = a.j
+          a.j = a.j-t;
+          t = u;
+          end;
+        end;
+      ol=''
+      Do k=n+1 to m
+        ol=ol a.k
+        End
+      Say n ol
+      End
+    End
+  Return