@ ProgramNode (location: (1,0)-(3,19))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(3,19))
    └── body: (length: 2)
        ├── @ CallNode (location: (1,0)-(1,20))
        │   ├── flags: ignore_visibility
        │   ├── receiver: ∅
        │   ├── call_operator_loc: ∅
        │   ├── name: :m
        │   ├── message_loc: (1,0)-(1,1) = "m"
        │   ├── opening_loc: ∅
        │   ├── arguments:
        │   │   @ ArgumentsNode (location: (1,2)-(1,20))
        │   │   ├── flags: ∅
        │   │   └── arguments: (length: 1)
        │   │       └── @ LambdaNode (location: (1,2)-(1,20))
        │   │           ├── locals: [:a]
        │   │           ├── operator_loc: (1,2)-(1,4) = "->"
        │   │           ├── opening_loc: (1,17)-(1,18) = "{"
        │   │           ├── closing_loc: (1,19)-(1,20) = "}"
        │   │           ├── parameters:
        │   │           │   @ BlockParametersNode (location: (1,4)-(1,16))
        │   │           │   ├── parameters:
        │   │           │   │   @ ParametersNode (location: (1,5)-(1,15))
        │   │           │   │   ├── requireds: (length: 0)
        │   │           │   │   ├── optionals: (length: 1)
        │   │           │   │   │   └── @ OptionalParameterNode (location: (1,5)-(1,15))
        │   │           │   │   │       ├── flags: ∅
        │   │           │   │   │       ├── name: :a
        │   │           │   │   │       ├── name_loc: (1,5)-(1,6) = "a"
        │   │           │   │   │       ├── operator_loc: (1,7)-(1,8) = "="
        │   │           │   │   │       └── value:
        │   │           │   │   │           @ LambdaNode (location: (1,9)-(1,15))
        │   │           │   │   │           ├── locals: [:_1]
        │   │           │   │   │           ├── operator_loc: (1,9)-(1,11) = "->"
        │   │           │   │   │           ├── opening_loc: (1,11)-(1,12) = "{"
        │   │           │   │   │           ├── closing_loc: (1,14)-(1,15) = "}"
        │   │           │   │   │           ├── parameters:
        │   │           │   │   │           │   @ NumberedParametersNode (location: (1,9)-(1,15))
        │   │           │   │   │           │   └── maximum: 1
        │   │           │   │   │           └── body:
        │   │           │   │   │               @ StatementsNode (location: (1,12)-(1,14))
        │   │           │   │   │               └── body: (length: 1)
        │   │           │   │   │                   └── @ LocalVariableReadNode (location: (1,12)-(1,14))
        │   │           │   │   │                       ├── name: :_1
        │   │           │   │   │                       └── depth: 0
        │   │           │   │   ├── rest: ∅
        │   │           │   │   ├── posts: (length: 0)
        │   │           │   │   ├── keywords: (length: 0)
        │   │           │   │   ├── keyword_rest: ∅
        │   │           │   │   └── block: ∅
        │   │           │   ├── locals: (length: 0)
        │   │           │   ├── opening_loc: (1,4)-(1,5) = "("
        │   │           │   └── closing_loc: (1,15)-(1,16) = ")"
        │   │           └── body:
        │   │               @ StatementsNode (location: (1,18)-(1,19))
        │   │               └── body: (length: 1)
        │   │                   └── @ LocalVariableReadNode (location: (1,18)-(1,19))
        │   │                       ├── name: :a
        │   │                       └── depth: 0
        │   ├── closing_loc: ∅
        │   └── block: ∅
        └── @ CallNode (location: (3,0)-(3,19))
            ├── flags: ignore_visibility
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── name: :m
            ├── message_loc: (3,0)-(3,1) = "m"
            ├── opening_loc: ∅
            ├── arguments:
            │   @ ArgumentsNode (location: (3,2)-(3,19))
            │   ├── flags: ∅
            │   └── arguments: (length: 1)
            │       └── @ LambdaNode (location: (3,2)-(3,19))
            │           ├── locals: [:a]
            │           ├── operator_loc: (3,2)-(3,4) = "->"
            │           ├── opening_loc: (3,16)-(3,17) = "{"
            │           ├── closing_loc: (3,18)-(3,19) = "}"
            │           ├── parameters:
            │           │   @ BlockParametersNode (location: (3,4)-(3,15))
            │           │   ├── parameters:
            │           │   │   @ ParametersNode (location: (3,5)-(3,14))
            │           │   │   ├── requireds: (length: 0)
            │           │   │   ├── optionals: (length: 0)
            │           │   │   ├── rest: ∅
            │           │   │   ├── posts: (length: 0)
            │           │   │   ├── keywords: (length: 1)
            │           │   │   │   └── @ OptionalKeywordParameterNode (location: (3,5)-(3,14))
            │           │   │   │       ├── flags: ∅
            │           │   │   │       ├── name: :a
            │           │   │   │       ├── name_loc: (3,5)-(3,7) = "a:"
            │           │   │   │       └── value:
            │           │   │   │           @ LambdaNode (location: (3,8)-(3,14))
            │           │   │   │           ├── locals: [:_1]
            │           │   │   │           ├── operator_loc: (3,8)-(3,10) = "->"
            │           │   │   │           ├── opening_loc: (3,10)-(3,11) = "{"
            │           │   │   │           ├── closing_loc: (3,13)-(3,14) = "}"
            │           │   │   │           ├── parameters:
            │           │   │   │           │   @ NumberedParametersNode (location: (3,8)-(3,14))
            │           │   │   │           │   └── maximum: 1
            │           │   │   │           └── body:
            │           │   │   │               @ StatementsNode (location: (3,11)-(3,13))
            │           │   │   │               └── body: (length: 1)
            │           │   │   │                   └── @ LocalVariableReadNode (location: (3,11)-(3,13))
            │           │   │   │                       ├── name: :_1
            │           │   │   │                       └── depth: 0
            │           │   │   ├── keyword_rest: ∅
            │           │   │   └── block: ∅
            │           │   ├── locals: (length: 0)
            │           │   ├── opening_loc: (3,4)-(3,5) = "("
            │           │   └── closing_loc: (3,14)-(3,15) = ")"
            │           └── body:
            │               @ StatementsNode (location: (3,17)-(3,18))
            │               └── body: (length: 1)
            │                   └── @ LocalVariableReadNode (location: (3,17)-(3,18))
            │                       ├── name: :a
            │                       └── depth: 0
            ├── closing_loc: ∅
            └── block: ∅