@ ProgramNode (location: (1,0)-(2,3))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(2,3))
    └── body: (length: 2)
        ├── @ CallNode (location: (1,0)-(2,1))
        │   ├── flags: ∅
        │   ├── receiver: ∅
        │   ├── call_operator_loc: ∅
        │   ├── name: :a
        │   ├── message_loc: (1,0)-(1,1) = "a"
        │   ├── opening_loc: ∅
        │   ├── arguments:
        │   │   @ ArgumentsNode (location: (1,2)-(2,1))
        │   │   ├── flags: ∅
        │   │   └── arguments: (length: 1)
        │   │       └── @ StringNode (location: (1,2)-(2,1))
        │   │           ├── flags: ∅
        │   │           ├── opening_loc: (1,2)-(1,3) = "'"
        │   │           ├── content_loc: (1,3)-(2,0) = "\n"
        │   │           ├── closing_loc: (2,0)-(2,1) = "'"
        │   │           └── unescaped: "\n"
        │   ├── closing_loc: ∅
        │   └── block: ∅
        └── @ CallNode (location: (2,2)-(2,3))
            ├── flags: variable_call
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── name: :b
            ├── message_loc: (2,2)-(2,3) = "b"
            ├── opening_loc: ∅
            ├── arguments: ∅
            ├── closing_loc: ∅
            └── block: ∅
