csharp71.cs:
#    1| [Class] DefaultLiterals
#    3|   5: [Method] f
#    3|     -1: [TypeMention] Void
#    4|     4: [BlockStmt] {...}
#    5|       0: [LocalVariableDeclStmt] ... ...;
#    5|         0: [LocalVariableDeclAndInitExpr] Int32 x = ...
#    5|           -1: [TypeMention] int
#    5|           0: [LocalVariableAccess] access to local variable x
#    5|           1: [CastExpr] (...) ...
#    5|             1: [DefaultValueExpr] default
#    5|         1: [LocalVariableDeclAndInitExpr] Int32 y = ...
#    5|           -1: [TypeMention] int
#    5|           0: [LocalVariableAccess] access to local variable y
#    5|           1: [DefaultValueExpr] default(...)
#    5|             0: [TypeAccess] access to type Int32
#    5|               0: [TypeMention] int
#    6|       1: [IfStmt] if (...) ...
#    6|         0: [EQExpr] ... == ...
#    6|           0: [LocalVariableAccess] access to local variable x
#    6|           1: [CastExpr] (...) ...
#    6|             1: [DefaultValueExpr] default
#    7|         1: [EmptyStmt] ;
#    8|       2: [SwitchStmt] switch (...) {...}
#    8|         0: [LocalVariableAccess] access to local variable x
#   10|         0: [CaseStmt] case ...:
#   10|           0: [DiscardPatternExpr] _
#   10|         1: [BreakStmt] break;
#   12|       3: [ExprStmt] ...;
#   12|         0: [AssignExpr] ... = ...
#   12|           0: [LocalVariableAccess] access to local variable x
#   12|           1: [CastExpr] (...) ...
#   12|             1: [DefaultValueExpr] default
#   13|       4: [LocalVariableDeclStmt] ... ...;
#   13|         0: [LocalVariableDeclAndInitExpr] String s = ...
#   13|           -1: [TypeMention] string
#   13|           0: [LocalVariableAccess] access to local variable s
#   13|           1: [CastExpr] (...) ...
#   13|             1: [DefaultValueExpr] default
#   14|       5: [LocalVariableDeclStmt] ... ...;
#   14|         0: [LocalVariableDeclAndInitExpr] Boolean b = ...
#   14|           -1: [TypeMention] bool
#   14|           0: [LocalVariableAccess] access to local variable b
#   14|           1: [CastExpr] (...) ...
#   14|             1: [DefaultValueExpr] default
#   15|       6: [LocalVariableDeclStmt] ... ...;
#   15|         0: [LocalVariableDeclAndInitExpr] Double d = ...
#   15|           -1: [TypeMention] double
#   15|           0: [LocalVariableAccess] access to local variable d
#   15|           1: [CastExpr] (...) ...
#   15|             1: [DefaultValueExpr] default
#   19| [Class] IsConstants
#   21|   5: [Method] f
#   21|     -1: [TypeMention] Void
#   22|     4: [BlockStmt] {...}
#   23|       0: [LocalVariableDeclStmt] ... ...;
#   23|         0: [LocalVariableDeclExpr] Boolean b
#   23|           0: [TypeMention] bool
#   24|       1: [ExprStmt] ...;
#   24|         0: [AssignExpr] ... = ...
#   24|           0: [LocalVariableAccess] access to local variable b
#   24|           1: [IsExpr] ... is ...
#   24|             0: [ObjectCreation] object creation of type Object
#   24|               0: [TypeMention] object
#   24|             1: [ConstantPatternExpr,StringLiteralUtf16] "abc"
#   25|       2: [ExprStmt] ...;
#   25|         0: [AssignExpr] ... = ...
#   25|           0: [LocalVariableAccess] access to local variable b
#   25|           1: [IsExpr] ... is ...
#   25|             0: [StringLiteralUtf16] ""
#   25|             1: [ConstantPatternExpr,NullLiteral] null
#   26|       3: [ExprStmt] ...;
#   26|         0: [AssignExpr] ... = ...
#   26|           0: [LocalVariableAccess] access to local variable b
#   26|           1: [IsExpr] ... is ...
#   26|             0: [LocalVariableAccess] access to local variable b
#   26|             1: [BoolLiteral,ConstantPatternExpr] true