0(1) element: null
1(2) WRITE ACCESS: x
2(3) element: PyMatchStatement
3(4) READ ACCESS: x
4(5,8) refutable pattern: 42
5(6) matched pattern: 42
6(7) ASSERTTYPE ACCESS: x
7(11) element: PyReturnStatement
8(9) ASSERTTYPE ACCESS: x
9(10) element: PyExpressionStatement
10(11) READ ACCESS: y
11() element: null