@ ProgramNode (location: (0...51))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...51))
    └── body: (length: 2)
        ├── @ DefNode (location: (0...23))
        │   ├── name: :foo
        │   ├── name_loc: (4...7) = "foo"
        │   ├── receiver: ∅
        │   ├── parameters:
        │   │   @ ParametersNode (location: (8...9))
        │   │   ├── requireds: (length: 0)
        │   │   ├── optionals: (length: 0)
        │   │   ├── rest: ∅
        │   │   ├── posts: (length: 0)
        │   │   ├── keywords: (length: 0)
        │   │   ├── keyword_rest: ∅
        │   │   └── block:
        │   │       @ BlockParameterNode (location: (8...9))
        │   │       ├── name: nil
        │   │       ├── name_loc: ∅
        │   │       └── operator_loc: (8...9) = "&"
        │   ├── body:
        │   │   @ StatementsNode (location: (13...19))
        │   │   └── body: (length: 1)
        │   │       └── @ CallNode (location: (13...19))
        │   │           ├── receiver: ∅
        │   │           ├── call_operator_loc: ∅
        │   │           ├── message_loc: (13...16) = "bar"
        │   │           ├── opening_loc: (16...17) = "("
        │   │           ├── arguments:
        │   │           │   @ ArgumentsNode (location: (17...18))
        │   │           │   └── arguments: (length: 1)
        │   │           │       └── @ BlockArgumentNode (location: (17...18))
        │   │           │           ├── expression: ∅
        │   │           │           └── operator_loc: (17...18) = "&"
        │   │           ├── closing_loc: (18...19) = ")"
        │   │           ├── block: ∅
        │   │           ├── flags: ∅
        │   │           └── name: "bar"
        │   ├── locals: [:&]
        │   ├── def_keyword_loc: (0...3) = "def"
        │   ├── operator_loc: ∅
        │   ├── lparen_loc: (7...8) = "("
        │   ├── rparen_loc: (9...10) = ")"
        │   ├── equal_loc: ∅
        │   └── end_keyword_loc: (20...23) = "end"
        └── @ DefNode (location: (25...51))
            ├── name: :foo
            ├── name_loc: (29...32) = "foo"
            ├── receiver: ∅
            ├── parameters:
            │   @ ParametersNode (location: (33...37))
            │   ├── requireds: (length: 1)
            │   │   └── @ RequiredParameterNode (location: (33...34))
            │   │       └── name: :a
            │   ├── optionals: (length: 0)
            │   ├── rest: ∅
            │   ├── posts: (length: 0)
            │   ├── keywords: (length: 0)
            │   ├── keyword_rest: ∅
            │   └── block:
            │       @ BlockParameterNode (location: (36...37))
            │       ├── name: nil
            │       ├── name_loc: ∅
            │       └── operator_loc: (36...37) = "&"
            ├── body:
            │   @ StatementsNode (location: (41...47))
            │   └── body: (length: 1)
            │       └── @ CallNode (location: (41...47))
            │           ├── receiver: ∅
            │           ├── call_operator_loc: ∅
            │           ├── message_loc: (41...44) = "bar"
            │           ├── opening_loc: (44...45) = "("
            │           ├── arguments:
            │           │   @ ArgumentsNode (location: (45...46))
            │           │   └── arguments: (length: 1)
            │           │       └── @ BlockArgumentNode (location: (45...46))
            │           │           ├── expression: ∅
            │           │           └── operator_loc: (45...46) = "&"
            │           ├── closing_loc: (46...47) = ")"
            │           ├── block: ∅
            │           ├── flags: ∅
            │           └── name: "bar"
            ├── locals: [:a, :&]
            ├── def_keyword_loc: (25...28) = "def"
            ├── operator_loc: ∅
            ├── lparen_loc: (32...33) = "("
            ├── rparen_loc: (37...38) = ")"
            ├── equal_loc: ∅
            └── end_keyword_loc: (48...51) = "end"
