@ ProgramNode (location: (1,0)-(1,19))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,19))
    └── body: (length: 1)
        └── @ DefNode (location: (1,0)-(1,19))
            ├── name: :exec
            ├── name_loc: (1,4)-(1,8) = "exec"
            ├── receiver: ∅
            ├── parameters: ∅
            ├── body:
            │   @ StatementsNode (location: (1,13)-(1,19))
            │   └── body: (length: 1)
            │       └── @ CallNode (location: (1,13)-(1,19))
            │           ├── flags: variable_call, ignore_visibility
            │           ├── receiver: ∅
            │           ├── call_operator_loc: ∅
            │           ├── name: :system
            │           ├── message_loc: (1,13)-(1,19) = "system"
            │           ├── opening_loc: ∅
            │           ├── arguments: ∅
            │           ├── closing_loc: ∅
            │           └── block: ∅
            ├── locals: []
            ├── def_keyword_loc: (1,0)-(1,3) = "def"
            ├── operator_loc: ∅
            ├── lparen_loc: (1,8)-(1,9) = "("
            ├── rparen_loc: (1,9)-(1,10) = ")"
            ├── equal_loc: (1,11)-(1,12) = "="
            └── end_keyword_loc: ∅