@ ProgramNode (location: (0...32))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...32))
    └── body: (length: 1)
        └── @ DefNode (location: (0...32))
            ├── name: :exec
            ├── name_loc: (9...13) = "exec"
            ├── receiver:
            │   @ SelfNode (location: (4...8))
            ├── parameters:
            │   @ ParametersNode (location: (14...17))
            │   ├── requireds: (length: 1)
            │   │   └── @ RequiredParameterNode (location: (14...17))
            │   │       └── name: :cmd
            │   ├── optionals: (length: 0)
            │   ├── rest: ∅
            │   ├── posts: (length: 0)
            │   ├── keywords: (length: 0)
            │   ├── keyword_rest: ∅
            │   └── block: ∅
            ├── body:
            │   @ StatementsNode (location: (21...32))
            │   └── body: (length: 1)
            │       └── @ CallNode (location: (21...32))
            │           ├── receiver: ∅
            │           ├── call_operator_loc: ∅
            │           ├── message_loc: (21...27) = "system"
            │           ├── opening_loc: (27...28) = "("
            │           ├── arguments:
            │           │   @ ArgumentsNode (location: (28...31))
            │           │   └── arguments: (length: 1)
            │           │       └── @ LocalVariableReadNode (location: (28...31))
            │           │           ├── name: :cmd
            │           │           └── depth: 0
            │           ├── closing_loc: (31...32) = ")"
            │           ├── block: ∅
            │           ├── flags: ∅
            │           └── name: "system"
            ├── locals: [:cmd]
            ├── def_keyword_loc: (0...3) = "def"
            ├── operator_loc: (8...9) = "."
            ├── lparen_loc: (13...14) = "("
            ├── rparen_loc: (17...18) = ")"
            ├── equal_loc: (19...20) = "="
            └── end_keyword_loc: ∅
