@ ProgramNode (location: (1,0)-(7,3))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(7,3))
    └── body: (length: 2)
        ├── @ DefNode (location: (1,0)-(3,3))
        │   ├── name: :foo
        │   ├── name_loc: (1,4)-(1,7) = "foo"
        │   ├── receiver: ∅
        │   ├── parameters:
        │   │   @ ParametersNode (location: (1,8)-(1,9))
        │   │   ├── requireds: (length: 0)
        │   │   ├── optionals: (length: 0)
        │   │   ├── rest: ∅
        │   │   ├── posts: (length: 0)
        │   │   ├── keywords: (length: 0)
        │   │   ├── keyword_rest: ∅
        │   │   └── block:
        │   │       @ BlockParameterNode (location: (1,8)-(1,9))
        │   │       ├── name: ∅
        │   │       ├── name_loc: ∅
        │   │       └── operator_loc: (1,8)-(1,9) = "&"
        │   ├── body:
        │   │   @ StatementsNode (location: (2,2)-(2,7))
        │   │   └── body: (length: 1)
        │   │       └── @ CallNode (location: (2,2)-(2,7))
        │   │           ├── flags: ∅
        │   │           ├── receiver: ∅
        │   │           ├── call_operator_loc: ∅
        │   │           ├── name: :bar
        │   │           ├── message_loc: (2,2)-(2,5) = "bar"
        │   │           ├── opening_loc: (2,5)-(2,6) = "("
        │   │           ├── arguments: ∅
        │   │           ├── closing_loc: (2,7)-(2,8) = ")"
        │   │           └── block:
        │   │               @ BlockArgumentNode (location: (2,6)-(2,7))
        │   │               ├── expression: ∅
        │   │               └── operator_loc: (2,6)-(2,7) = "&"
        │   ├── locals: [:&]
        │   ├── locals_body_index: 1
        │   ├── def_keyword_loc: (1,0)-(1,3) = "def"
        │   ├── operator_loc: ∅
        │   ├── lparen_loc: (1,7)-(1,8) = "("
        │   ├── rparen_loc: (1,9)-(1,10) = ")"
        │   ├── equal_loc: ∅
        │   └── end_keyword_loc: (3,0)-(3,3) = "end"
        └── @ DefNode (location: (5,0)-(7,3))
            ├── name: :foo
            ├── name_loc: (5,4)-(5,7) = "foo"
            ├── receiver: ∅
            ├── parameters:
            │   @ ParametersNode (location: (5,8)-(5,12))
            │   ├── requireds: (length: 1)
            │   │   └── @ RequiredParameterNode (location: (5,8)-(5,9))
            │   │       └── name: :a
            │   ├── optionals: (length: 0)
            │   ├── rest: ∅
            │   ├── posts: (length: 0)
            │   ├── keywords: (length: 0)
            │   ├── keyword_rest: ∅
            │   └── block:
            │       @ BlockParameterNode (location: (5,11)-(5,12))
            │       ├── name: ∅
            │       ├── name_loc: ∅
            │       └── operator_loc: (5,11)-(5,12) = "&"
            ├── body:
            │   @ StatementsNode (location: (6,2)-(6,7))
            │   └── body: (length: 1)
            │       └── @ CallNode (location: (6,2)-(6,7))
            │           ├── flags: ∅
            │           ├── receiver: ∅
            │           ├── call_operator_loc: ∅
            │           ├── name: :bar
            │           ├── message_loc: (6,2)-(6,5) = "bar"
            │           ├── opening_loc: (6,5)-(6,6) = "("
            │           ├── arguments: ∅
            │           ├── closing_loc: (6,7)-(6,8) = ")"
            │           └── block:
            │               @ BlockArgumentNode (location: (6,6)-(6,7))
            │               ├── expression: ∅
            │               └── operator_loc: (6,6)-(6,7) = "&"
            ├── locals: [:a, :&]
            ├── locals_body_index: 2
            ├── def_keyword_loc: (5,0)-(5,3) = "def"
            ├── operator_loc: ∅
            ├── lparen_loc: (5,7)-(5,8) = "("
            ├── rparen_loc: (5,12)-(5,13) = ")"
            ├── equal_loc: ∅
            └── end_keyword_loc: (7,0)-(7,3) = "end"