@ ProgramNode (location: (1,0)-(4,3))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(4,3))
    └── body: (length: 1)
        └── @ CallNode (location: (1,0)-(4,3))
            ├── flags: ∅
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── name: :x
            ├── message_loc: (1,0)-(1,1) = "x"
            ├── opening_loc: ∅
            ├── arguments:
            │   @ ArgumentsNode (location: (1,2)-(4,3))
            │   ├── flags: ∅
            │   └── arguments: (length: 1)
            │       └── @ LambdaNode (location: (1,2)-(4,3))
            │           ├── locals: []
            │           ├── locals_body_index: 0
            │           ├── operator_loc: (1,2)-(1,4) = "->"
            │           ├── opening_loc: (1,8)-(1,10) = "do"
            │           ├── closing_loc: (4,0)-(4,3) = "end"
            │           ├── parameters:
            │           │   @ BlockParametersNode (location: (1,5)-(1,7))
            │           │   ├── parameters: ∅
            │           │   ├── locals: (length: 0)
            │           │   ├── opening_loc: (1,5)-(1,6) = "("
            │           │   └── closing_loc: (1,6)-(1,7) = ")"
            │           └── body:
            │               @ StatementsNode (location: (2,0)-(3,3))
            │               └── body: (length: 1)
            │                   └── @ CallNode (location: (2,0)-(3,3))
            │                       ├── flags: ∅
            │                       ├── receiver:
            │                       │   @ CallNode (location: (2,0)-(2,1))
            │                       │   ├── flags: variable_call
            │                       │   ├── receiver: ∅
            │                       │   ├── call_operator_loc: ∅
            │                       │   ├── name: :a
            │                       │   ├── message_loc: (2,0)-(2,1) = "a"
            │                       │   ├── opening_loc: ∅
            │                       │   ├── arguments: ∅
            │                       │   ├── closing_loc: ∅
            │                       │   └── block: ∅
            │                       ├── call_operator_loc: (2,1)-(2,2) = "."
            │                       ├── name: :b
            │                       ├── message_loc: (2,2)-(2,3) = "b"
            │                       ├── opening_loc: ∅
            │                       ├── arguments: ∅
            │                       ├── closing_loc: ∅
            │                       └── block:
            │                           @ BlockNode (location: (2,4)-(3,3))
            │                           ├── locals: []
            │                           ├── locals_body_index: 0
            │                           ├── parameters: ∅
            │                           ├── body: ∅
            │                           ├── opening_loc: (2,4)-(2,6) = "do"
            │                           └── closing_loc: (3,0)-(3,3) = "end"
            ├── closing_loc: ∅
            └── block: ∅
