@ ProgramNode (location: (1,0)-(1,15))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,15))
    └── body: (length: 1)
        └── @ CallNode (location: (1,0)-(1,15))
            ├── flags: ∅
            ├── receiver:
            │   @ CallNode (location: (1,0)-(1,12))
            │   ├── 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: (1,1)-(1,2) = "."
            │   ├── name: :b
            │   ├── message_loc: (1,2)-(1,3) = "b"
            │   ├── opening_loc: ∅
            │   ├── arguments:
            │   │   @ ArgumentsNode (location: (1,4)-(1,5))
            │   │   ├── flags: ∅
            │   │   └── arguments: (length: 1)
            │   │       └── @ CallNode (location: (1,4)-(1,5))
            │   │           ├── flags: variable_call
            │   │           ├── receiver: ∅
            │   │           ├── call_operator_loc: ∅
            │   │           ├── name: :c
            │   │           ├── message_loc: (1,4)-(1,5) = "c"
            │   │           ├── opening_loc: ∅
            │   │           ├── arguments: ∅
            │   │           ├── closing_loc: ∅
            │   │           └── block: ∅
            │   ├── closing_loc: ∅
            │   └── block:
            │       @ BlockNode (location: (1,6)-(1,12))
            │       ├── locals: []
            │       ├── locals_body_index: 0
            │       ├── parameters: ∅
            │       ├── body: ∅
            │       ├── opening_loc: (1,6)-(1,8) = "do"
            │       └── closing_loc: (1,9)-(1,12) = "end"
            ├── call_operator_loc: (1,12)-(1,14) = "::"
            ├── name: :d
            ├── message_loc: (1,14)-(1,15) = "d"
            ├── opening_loc: ∅
            ├── arguments: ∅
            ├── closing_loc: ∅
            └── block: ∅
