Added a test for self-erasing token

examples/tests.modal

@@ -1,9 +1,5 @@
 ?(?-) (This example tests various aspects of the implementation.)
 
-<> (?: print) (?:)
-<> (?x = ?x test) (#ok)
-<> (?x = ?y test) (#fail)
-
 ?(?-) (Inline rules)
 
 <> ((?x -> ?y)) (<> ?x ?y)
@@ -19,7 +15,7 @@ nap tap test
 
 abc def pop-plain = abc test
 abc def pop = abc test
-(ghost) = ()
+(ghost) = () test
 
 ?(?-) (Basic replacements)
 
@@ -68,6 +64,12 @@ explode (12 34 45) (12 (34 (45 ()))) test
 implode (b (a (t ()))) bat test
 implode (12 (34 (56 ()))) 123456 test
 
+?(?-) (Test Primitives)
+
+<> (?: print) (?:)
+<> (?x = ?x test) (#ok)
+<> (?x = ?y test) (#fail)
+
 ?(?-) (List reversal)
 
 <> (reverse List () ?^) (?^)
@@ -75,3 +77,4 @@ implode (12 (34 (56 ()))) 123456 test
 <> (reverse List (?x ?y) ?z) (reverse List ?y (?x ?z))
 
 reverse (modal) = ladom test
+