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