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