csharp71.cs:
#    3| [Class] DefaultLiterals
#    5|   5: [Method] f
#    5|     -1: [TypeMention] Void
#    6|     4: [BlockStmt] {...}
#    7|       0: [LocalVariableDeclStmt] ... ...;
#    7|         0: [LocalVariableDeclAndInitExpr] Int32 x = ...
#    7|           -1: [TypeMention] int
#    7|           0: [LocalVariableAccess] access to local variable x
#    7|           1: [CastExpr] (...) ...
#    7|             1: [DefaultValueExpr] default
#    7|         1: [LocalVariableDeclAndInitExpr] Int32 y = ...
#    7|           -1: [TypeMention] int
#    7|           0: [LocalVariableAccess] access to local variable y
#    7|           1: [DefaultValueExpr] default(...)
#    7|             0: [TypeAccess] access to type Int32
#    7|               0: [TypeMention] int
#    8|       1: [IfStmt] if (...) ...
#    8|         0: [EQExpr] ... == ...
#    8|           0: [LocalVariableAccess] access to local variable x
#    8|           1: [CastExpr] (...) ...
#    8|             1: [DefaultValueExpr] default
#    9|         1: [EmptyStmt] ;
#   10|       2: [SwitchStmt] switch (...) {...}
#   10|         0: [LocalVariableAccess] access to local variable x
#   12|         0: [CaseStmt] case ...:
#   12|           0: [DiscardPatternExpr] _
#   12|         1: [BreakStmt] break;
#   14|       3: [ExprStmt] ...;
#   14|         0: [AssignExpr] ... = ...
#   14|           0: [LocalVariableAccess] access to local variable x
#   14|           1: [CastExpr] (...) ...
#   14|             1: [DefaultValueExpr] default
#   15|       4: [LocalVariableDeclStmt] ... ...;
#   15|         0: [LocalVariableDeclAndInitExpr] String s = ...
#   15|           -1: [TypeMention] string
#   15|           0: [LocalVariableAccess] access to local variable s
#   15|           1: [CastExpr] (...) ...
#   15|             1: [DefaultValueExpr] default
#   16|       5: [LocalVariableDeclStmt] ... ...;
#   16|         0: [LocalVariableDeclAndInitExpr] Boolean b = ...
#   16|           -1: [TypeMention] bool
#   16|           0: [LocalVariableAccess] access to local variable b
#   16|           1: [CastExpr] (...) ...
#   16|             1: [DefaultValueExpr] default
#   17|       6: [LocalVariableDeclStmt] ... ...;
#   17|         0: [LocalVariableDeclAndInitExpr] Double d = ...
#   17|           -1: [TypeMention] double
#   17|           0: [LocalVariableAccess] access to local variable d
#   17|           1: [CastExpr] (...) ...
#   17|             1: [DefaultValueExpr] default
#   21| [Class] IsConstants
#   23|   5: [Method] f
#   23|     -1: [TypeMention] Void
#   24|     4: [BlockStmt] {...}
#   25|       0: [LocalVariableDeclStmt] ... ...;
#   25|         0: [LocalVariableDeclExpr] Boolean b
#   25|           0: [TypeMention] bool
#   26|       1: [ExprStmt] ...;
#   26|         0: [AssignExpr] ... = ...
#   26|           0: [LocalVariableAccess] access to local variable b
#   26|           1: [IsExpr] ... is ...
#   26|             0: [ObjectCreation] object creation of type Object
#   26|               0: [TypeMention] object
#   26|             1: [ConstantPatternExpr,StringLiteral] "abc"
#   27|       2: [ExprStmt] ...;
#   27|         0: [AssignExpr] ... = ...
#   27|           0: [LocalVariableAccess] access to local variable b
#   27|           1: [IsExpr] ... is ...
#   27|             0: [StringLiteral] ""
#   27|             1: [ConstantPatternExpr,NullLiteral] null
#   28|       3: [ExprStmt] ...;
#   28|         0: [AssignExpr] ... = ...
#   28|           0: [LocalVariableAccess] access to local variable b
#   28|           1: [IsExpr] ... is ...
#   28|             0: [LocalVariableAccess] access to local variable b
#   28|             1: [BoolLiteral,ConstantPatternExpr] true