@ ProgramNode (location: (1,0)-(1,27))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,27))
    └── body: (length: 1)
        └── @ ReturnNode (location: (1,0)-(1,27))
            ├── flags: ∅
            ├── keyword_loc: (1,0)-(1,6) = "return"
            └── arguments:
                @ ArgumentsNode (location: (1,7)-(1,27))
                ├── flags: ∅
                └── arguments: (length: 1)
                    └── @ CallNode (location: (1,7)-(1,27))
                        ├── flags: ignore_visibility
                        ├── receiver: ∅
                        ├── call_operator_loc: ∅
                        ├── name: :foo
                        ├── message_loc: (1,7)-(1,10) = "foo"
                        ├── opening_loc: ∅
                        ├── arguments:
                        │   @ ArgumentsNode (location: (1,11)-(1,14))
                        │   ├── flags: ∅
                        │   └── arguments: (length: 1)
                        │       └── @ CallNode (location: (1,11)-(1,14))
                        │           ├── flags: variable_call, ignore_visibility
                        │           ├── receiver: ∅
                        │           ├── call_operator_loc: ∅
                        │           ├── name: :arg
                        │           ├── message_loc: (1,11)-(1,14) = "arg"
                        │           ├── opening_loc: ∅
                        │           ├── arguments: ∅
                        │           ├── closing_loc: ∅
                        │           └── block: ∅
                        ├── closing_loc: ∅
                        └── block:
                            @ BlockNode (location: (1,15)-(1,27))
                            ├── locals: [:bar]
                            ├── parameters:
                            │   @ BlockParametersNode (location: (1,18)-(1,23))
                            │   ├── parameters:
                            │   │   @ ParametersNode (location: (1,19)-(1,22))
                            │   │   ├── requireds: (length: 1)
                            │   │   │   └── @ RequiredParameterNode (location: (1,19)-(1,22))
                            │   │   │       ├── flags: ∅
                            │   │   │       └── name: :bar
                            │   │   ├── optionals: (length: 0)
                            │   │   ├── rest: ∅
                            │   │   ├── posts: (length: 0)
                            │   │   ├── keywords: (length: 0)
                            │   │   ├── keyword_rest: ∅
                            │   │   └── block: ∅
                            │   ├── locals: (length: 0)
                            │   ├── opening_loc: (1,18)-(1,19) = "|"
                            │   └── closing_loc: (1,22)-(1,23) = "|"
                            ├── body: ∅
                            ├── opening_loc: (1,15)-(1,17) = "do"
                            └── closing_loc: (1,24)-(1,27) = "end"