@ ProgramNode (location: (1,0)-(1,19))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,19))
    └── body: (length: 1)
        └── @ NextNode (location: (1,0)-(1,19))
            ├── arguments:
            │   @ ArgumentsNode (location: (1,5)-(1,19))
            │   └── arguments: (length: 1)
            │       └── @ CallNode (location: (1,5)-(1,19))
            │           ├── receiver: ∅
            │           ├── call_operator_loc: ∅
            │           ├── message_loc: (1,5)-(1,8) = "fun"
            │           ├── opening_loc: ∅
            │           ├── arguments:
            │           │   @ ArgumentsNode (location: (1,9)-(1,12))
            │           │   └── arguments: (length: 1)
            │           │       └── @ CallNode (location: (1,9)-(1,12))
            │           │           ├── receiver: ∅
            │           │           ├── call_operator_loc: ∅
            │           │           ├── message_loc: (1,9)-(1,12) = "foo"
            │           │           ├── opening_loc: ∅
            │           │           ├── arguments: ∅
            │           │           ├── closing_loc: ∅
            │           │           ├── block: ∅
            │           │           ├── flags: variable_call
            │           │           └── name: :foo
            │           ├── closing_loc: ∅
            │           ├── block:
            │           │   @ BlockNode (location: (1,13)-(1,19))
            │           │   ├── locals: []
            │           │   ├── parameters: ∅
            │           │   ├── body: ∅
            │           │   ├── opening_loc: (1,13)-(1,15) = "do"
            │           │   └── closing_loc: (1,16)-(1,19) = "end"
            │           ├── flags: ∅
            │           └── name: :fun
            └── keyword_loc: (1,0)-(1,4) = "next"
