@ ProgramNode (location: (1,0)-(1,6))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,6))
    └── body: (length: 1)
        └── @ CallNode (location: (1,0)-(1,6))
            ├── flags: ignore_visibility
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── name: :x
            ├── message_loc: (1,0)-(1,1) = "x"
            ├── opening_loc: (1,1)-(1,2) = "("
            ├── arguments: ∅
            ├── closing_loc: (1,6)-(1,7) = ")"
            └── block:
                @ BlockArgumentNode (location: (1,2)-(1,6))
                ├── expression:
                │   @ CallNode (location: (1,3)-(1,6))
                │   ├── flags: variable_call, ignore_visibility
                │   ├── receiver: ∅
                │   ├── call_operator_loc: ∅
                │   ├── name: :blk
                │   ├── message_loc: (1,3)-(1,6) = "blk"
                │   ├── opening_loc: ∅
                │   ├── arguments: ∅
                │   ├── closing_loc: ∅
                │   └── block: ∅
                └── operator_loc: (1,2)-(1,3) = "&"