@ ProgramNode (location: (0...11))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...11))
    └── body: (length: 1)
        └── @ StringConcatNode (location: (0...11))
            ├── left:
            │   @ StringNode (location: (0...3))
            │   ├── opening_loc: (0...1) = "\""
            │   ├── content_loc: (1...2) = "a"
            │   ├── closing_loc: (2...3) = "\""
            │   └── unescaped: "a"
            └── right:
                @ InterpolatedStringNode (location: (5...11))
                ├── opening_loc: (5...6) = "\""
                ├── parts: (length: 1)
                │   └── @ EmbeddedStatementsNode (location: (6...10))
                │       ├── opening_loc: (6...8) = "\#{"
                │       ├── statements:
                │       │   @ StatementsNode (location: (8...9))
                │       │   └── body: (length: 1)
                │       │       └── @ CallNode (location: (8...9))
                │       │           ├── receiver: ∅
                │       │           ├── call_operator_loc: ∅
                │       │           ├── message_loc: (8...9) = "b"
                │       │           ├── opening_loc: ∅
                │       │           ├── arguments: ∅
                │       │           ├── closing_loc: ∅
                │       │           ├── block: ∅
                │       │           ├── flags: variable_call
                │       │           └── name: "b"
                │       └── closing_loc: (9...10) = "}"
                └── closing_loc: (10...11) = "\""
