Don't append return to void procedures

example.elna

@@ -79,17 +79,30 @@ begin
 end;
 
 proc test_if();
-var y: Bool;
+var x: Bool, y: Bool;
 begin
+  x := true;
   y := false;
 
   writei("");
-  if y then
+  if x and y then
     writei("Test if: True")
   else
     writei("Test if: False")
 end;
 
+proc test_not();
+var x: Bool;
+begin
+  x := false;
+
+  writei("");
+  if not x then
+    writei("Test not true.")
+  else
+    writei("Test not false")
+end;
+
 begin
   test_primitive();
   test_string();
@@ -97,5 +110,6 @@ begin
   test_pointer();
   test_record();
   test_const();
-  test_if()
+  test_if();
+  test_not()
 end.