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