@ ProgramNode (location: (1,0)-(4,2))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(4,2))
    └── body: (length: 1)
        └── @ CallNode (location: (1,0)-(4,2))
            ├── flags: ∅
            ├── receiver:
            │   @ CallNode (location: (1,0)-(2,2))
            │   ├── flags: ∅
            │   ├── receiver:
            │   │   @ CallNode (location: (1,0)-(1,1))
            │   │   ├── flags: variable_call
            │   │   ├── receiver: ∅
            │   │   ├── call_operator_loc: ∅
            │   │   ├── name: :a
            │   │   ├── message_loc: (1,0)-(1,1) = "a"
            │   │   ├── opening_loc: ∅
            │   │   ├── arguments: ∅
            │   │   ├── closing_loc: ∅
            │   │   └── block: ∅
            │   ├── call_operator_loc: (2,0)-(2,1) = "."
            │   ├── name: :b
            │   ├── message_loc: (2,1)-(2,2) = "b"
            │   ├── opening_loc: ∅
            │   ├── arguments: ∅
            │   ├── closing_loc: ∅
            │   └── block: ∅
            ├── call_operator_loc: (4,0)-(4,1) = "."
            ├── name: :d
            ├── message_loc: (4,1)-(4,2) = "d"
            ├── opening_loc: ∅
            ├── arguments: ∅
            ├── closing_loc: ∅
            └── block: ∅
