added for loop to test trivial cases and a comically slow python script to generate all potential test cases up to some number of ops

.gitignore

@@ -3,3 +3,4 @@ s
 t
 a.out
 .clangd
+tests

gen_track_cases.py

@@ -0,0 +1,37 @@
+import itertools
+from enum import Enum
+
+
+class Operation(Enum):
+    SUB = 0
+    ADD = 1
+
+    def __str__(self):
+        if self == Operation.SUB:
+            return "[]"
+        elif self == Operation.ADD:
+            return "()"
+        else:
+            raise Exception("unreachable")
+
+    def __radd__(self, num):
+        if self == Operation.SUB:
+            return num - 1
+        elif self == Operation.ADD:
+            return num + 1
+        else:
+            raise Exception("unreachable")
+
+
+track = set()
+
+for i in range(13):
+    ops_iter = itertools.combinations([Operation.ADD] * i + [Operation.SUB] * i, i)
+    for ops in ops_iter:
+        correct = sum(ops)
+        track.add(f"""i = a{"".join(str(op) for op in ops)};
+assert(i == {correct});""")
+
+with open("tests", "w+") as out:
+    for test in sorted(track):
+        print(test, file=out)

track.cpp

@@ -31,9 +31,201 @@ int main(void) {
   assert(a[] == -1);
   assert(a[]() == 0);
   assert(a[]()() == 1);
+  for (long long j = 1; j < 100; j++) {
+    A a2;
+    A a3;
+    for (long long k = 0; k < j; k++) {
+      assert(a2 == k);
+      assert(a3 == -k);
+      a2 = a2();
+      a3 = a3[];
+    }
+    assert(a2 == j);
+    assert(a3 == -j);
+  }
   int i = a;
   assert(i == 0);
+  i = a()()()()()()()()()()()();
+  assert(i == 12);
+  i = a()()()()()()()()()()();
+  assert(i == 11);
+  i = a()()()()()()()()()()()[];
+  assert(i == 10);
+  i = a()()()()()()()()()();
+  assert(i == 10);
+  i = a()()()()()()()()()()[];
+  assert(i == 9);
+  i = a()()()()()()()()()()[][];
+  assert(i == 8);
+  i = a()()()()()()()()();
+  assert(i == 9);
+  i = a()()()()()()()()()[];
+  assert(i == 8);
+  i = a()()()()()()()()()[][];
+  assert(i == 7);
+  i = a()()()()()()()()()[][][];
+  assert(i == 6);
+  i = a()()()()()()()();
+  assert(i == 8);
+  i = a()()()()()()()()[];
+  assert(i == 7);
+  i = a()()()()()()()()[][];
+  assert(i == 6);
+  i = a()()()()()()()()[][][];
+  assert(i == 5);
+  i = a()()()()()()()()[][][][];
+  assert(i == 4);
+  i = a()()()()()()();
+  assert(i == 7);
+  i = a()()()()()()()[];
+  assert(i == 6);
+  i = a()()()()()()()[][];
+  assert(i == 5);
+  i = a()()()()()()()[][][];
+  assert(i == 4);
+  i = a()()()()()()()[][][][];
+  assert(i == 3);
+  i = a()()()()()()()[][][][][];
+  assert(i == 2);
+  i = a()()()()()();
+  assert(i == 6);
+  i = a()()()()()()[];
+  assert(i == 5);
+  i = a()()()()()()[][];
+  assert(i == 4);
+  i = a()()()()()()[][][];
+  assert(i == 3);
+  i = a()()()()()()[][][][];
+  assert(i == 2);
+  i = a()()()()()()[][][][][];
+  assert(i == 1);
+  i = a()()()()()()[][][][][][];
+  assert(i == 0);
+  i = a()()()()();
+  assert(i == 5);
+  i = a()()()()()[];
+  assert(i == 4);
+  i = a()()()()()[][];
+  assert(i == 3);
+  i = a()()()()()[][][];
+  assert(i == 2);
+  i = a()()()()()[][][][];
+  assert(i == 1);
+  i = a()()()()()[][][][][];
+  assert(i == 0);
+  i = a()()()()()[][][][][][];
+  assert(i == -1);
+  i = a()()()()()[][][][][][][];
+  assert(i == -2);
+  i = a()()()();
+  assert(i == 4);
+  i = a()()()()[];
+  assert(i == 3);
+  i = a()()()()[][];
+  assert(i == 2);
+  i = a()()()()[][][];
+  assert(i == 1);
+  i = a()()()()[][][][];
+  assert(i == 0);
+  i = a()()()()[][][][][];
+  assert(i == -1);
+  i = a()()()()[][][][][][];
+  assert(i == -2);
+  i = a()()()()[][][][][][][];
+  assert(i == -3);
+  i = a()()()()[][][][][][][][];
+  assert(i == -4);
   i = a()()();
   assert(i == 3);
+  i = a()()()[];
+  assert(i == 2);
+  i = a()()()[][];
+  assert(i == 1);
+  i = a()()()[][][];
+  assert(i == 0);
+  i = a()()()[][][][];
+  assert(i == -1);
+  i = a()()()[][][][][];
+  assert(i == -2);
+  i = a()()()[][][][][][];
+  assert(i == -3);
+  i = a()()()[][][][][][][];
+  assert(i == -4);
+  i = a()()()[][][][][][][][];
+  assert(i == -5);
+  i = a()()()[][][][][][][][][];
+  assert(i == -6);
+  i = a()();
+  assert(i == 2);
+  i = a()()[];
+  assert(i == 1);
+  i = a()()[][];
+  assert(i == 0);
+  i = a()()[][][];
+  assert(i == -1);
+  i = a()()[][][][];
+  assert(i == -2);
+  i = a()()[][][][][];
+  assert(i == -3);
+  i = a()()[][][][][][];
+  assert(i == -4);
+  i = a()()[][][][][][][];
+  assert(i == -5);
+  i = a()()[][][][][][][][];
+  assert(i == -6);
+  i = a()()[][][][][][][][][];
+  assert(i == -7);
+  i = a()()[][][][][][][][][][];
+  assert(i == -8);
+  i = a();
+  assert(i == 1);
+  i = a()[];
+  assert(i == 0);
+  i = a()[][];
+  assert(i == -1);
+  i = a()[][][];
+  assert(i == -2);
+  i = a()[][][][];
+  assert(i == -3);
+  i = a()[][][][][];
+  assert(i == -4);
+  i = a()[][][][][][];
+  assert(i == -5);
+  i = a()[][][][][][][];
+  assert(i == -6);
+  i = a()[][][][][][][][];
+  assert(i == -7);
+  i = a()[][][][][][][][][];
+  assert(i == -8);
+  i = a()[][][][][][][][][][];
+  assert(i == -9);
+  i = a()[][][][][][][][][][][];
+  assert(i == -10);
+  i = a;
+  assert(i == 0);
+  i = a[];
+  assert(i == -1);
+  i = a[][];
+  assert(i == -2);
+  i = a[][][];
+  assert(i == -3);
+  i = a[][][][];
+  assert(i == -4);
+  i = a[][][][][];
+  assert(i == -5);
+  i = a[][][][][][];
+  assert(i == -6);
+  i = a[][][][][][][];
+  assert(i == -7);
+  i = a[][][][][][][][];
+  assert(i == -8);
+  i = a[][][][][][][][][];
+  assert(i == -9);
+  i = a[][][][][][][][][][];
+  assert(i == -10);
+  i = a[][][][][][][][][][][];
+  assert(i == -11);
+  i = a[][][][][][][][][][][][];
+  assert(i == -12);
   return 0;
 }