@ ProgramNode (location: (1,0)-(1,3))
├── flags: ∅
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,3))
    ├── flags: ∅
    └── body: (length: 1)
        └── @ CallNode (location: (1,0)-(1,3))
            ├── flags: newline
            ├── receiver:
            │   @ SymbolNode (location: (1,1)-(1,3))
            │   ├── flags: static_literal, forced_us_ascii_encoding
            │   ├── opening_loc: (1,1)-(1,2) = ":"
            │   ├── value_loc: (1,2)-(1,3) = "a"
            │   ├── closing_loc: ∅
            │   └── unescaped: "a"
            ├── call_operator_loc: ∅
            ├── name: :+@
            ├── message_loc: (1,0)-(1,1) = "+"
            ├── opening_loc: ∅
            ├── arguments: ∅
            ├── closing_loc: ∅
            └── block: ∅
