A-M baby

Task/Ackermann-function/Modula-2/ackermann-function.mod2

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+MODULE ackerman;
+
+IMPORT  ASCII, NumConv, InOut;
+
+VAR     m, n            : LONGCARD;
+        string          : ARRAY [0..19] OF CHAR;
+        OK              : BOOLEAN;
+
+PROCEDURE Ackerman (x, y   : LONGCARD) : LONGCARD;
+
+BEGIN
+  IF    x = 0  THEN  RETURN  y + 1
+  ELSIF y = 0  THEN  RETURN  Ackerman (x - 1 , 1)
+  ELSE
+    RETURN  Ackerman (x - 1 , Ackerman (x , y - 1))
+  END
+END Ackerman;
+
+BEGIN
+  FOR  m := 0  TO  3  DO
+    FOR  n := 0  TO  6  DO
+      NumConv.Num2Str (Ackerman (m, n), 10, string, OK);
+      IF  OK  THEN
+        InOut.WriteString (string)
+      ELSE
+        InOut.WriteString ("* Error in number * ")
+      END;
+      InOut.Write (ASCII.HT)
+    END;
+    InOut.WriteLn
+  END;
+  InOut.WriteLn
+END ackerman.