@ ProgramNode (location: (0...8))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...8))
    └── body: (length: 1)
        └── @ InterpolatedStringNode (location: (0...8))
            ├── opening_loc: (0...1) = "\""
            ├── parts: (length: 2)
            │   ├── @ EmbeddedStatementsNode (location: (1...5))
            │   │   ├── opening_loc: (1...3) = "\#{"
            │   │   ├── statements:
            │   │   │   @ StatementsNode (location: (3...4))
            │   │   │   └── body: (length: 1)
            │   │   │       └── @ CallNode (location: (3...4))
            │   │   │           ├── receiver: ∅
            │   │   │           ├── call_operator_loc: ∅
            │   │   │           ├── message_loc: (3...4) = "a"
            │   │   │           ├── opening_loc: ∅
            │   │   │           ├── arguments: ∅
            │   │   │           ├── closing_loc: ∅
            │   │   │           ├── block: ∅
            │   │   │           ├── flags: variable_call
            │   │   │           └── name: "a"
            │   │   └── closing_loc: (4...5) = "}"
            │   └── @ StringNode (location: (5...7))
            │       ├── opening_loc: ∅
            │       ├── content_loc: (5...7) = " b"
            │       ├── closing_loc: ∅
            │       └── unescaped: " b"
            └── closing_loc: (7...8) = "\""
