@ ProgramNode (location: (1,0)-(2,3))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(2,3))
    └── body: (length: 1)
        └── @ IfNode (location: (1,0)-(2,3))
            ├── if_keyword_loc: (1,0)-(1,2) = "if"
            ├── predicate:
            │   @ CallNode (location: (1,3)-(1,15))
            │   ├── flags: ∅
            │   ├── receiver:
            │   │   @ CallNode (location: (1,7)-(1,15))
            │   │   ├── flags: ∅
            │   │   ├── receiver:
            │   │   │   @ CallNode (location: (1,7)-(1,10))
            │   │   │   ├── flags: variable_call, ignore_visibility
            │   │   │   ├── receiver: ∅
            │   │   │   ├── call_operator_loc: ∅
            │   │   │   ├── name: :var
            │   │   │   ├── message_loc: (1,7)-(1,10) = "var"
            │   │   │   ├── opening_loc: ∅
            │   │   │   ├── arguments: ∅
            │   │   │   ├── closing_loc: ∅
            │   │   │   └── block: ∅
            │   │   ├── call_operator_loc: (1,10)-(1,11) = "."
            │   │   ├── name: :nil?
            │   │   ├── message_loc: (1,11)-(1,15) = "nil?"
            │   │   ├── opening_loc: ∅
            │   │   ├── arguments: ∅
            │   │   ├── closing_loc: ∅
            │   │   └── block: ∅
            │   ├── call_operator_loc: ∅
            │   ├── name: :!
            │   ├── message_loc: (1,3)-(1,6) = "not"
            │   ├── opening_loc: ∅
            │   ├── arguments: ∅
            │   ├── closing_loc: ∅
            │   └── block: ∅
            ├── then_keyword_loc: (1,16)-(1,20) = "then"
            ├── statements:
            │   @ StatementsNode (location: (1,21)-(1,26))
            │   └── body: (length: 1)
            │       └── @ StringNode (location: (1,21)-(1,26))
            │           ├── flags: ∅
            │           ├── opening_loc: (1,21)-(1,22) = "'"
            │           ├── content_loc: (1,22)-(1,25) = "foo"
            │           ├── closing_loc: (1,25)-(1,26) = "'"
            │           └── unescaped: "foo"
            ├── consequent:
            │   @ ElseNode (location: (1,27)-(2,3))
            │   ├── else_keyword_loc: (1,27)-(1,31) = "else"
            │   ├── statements:
            │   │   @ StatementsNode (location: (1,32)-(1,37))
            │   │   └── body: (length: 1)
            │   │       └── @ StringNode (location: (1,32)-(1,37))
            │   │           ├── flags: ∅
            │   │           ├── opening_loc: (1,32)-(1,33) = "'"
            │   │           ├── content_loc: (1,33)-(1,36) = "bar"
            │   │           ├── closing_loc: (1,36)-(1,37) = "'"
            │   │           └── unescaped: "bar"
            │   └── end_keyword_loc: (2,0)-(2,3) = "end"
            └── end_keyword_loc: (2,0)-(2,3) = "end"