| FunExpr Pos String [Expr] [FieldSelector]
| EmptyListExpr Pos
| TupleExpr Pos (Expr, Expr)
+ | LambdaExpr Pos [String] Expr
:: VarDef = VarDef String [FieldSelector]
:: FieldSelector = FieldHd | FieldTl | FieldFst | FieldSnd
:: Op1 = UnNegation | UnMinus
instance toString Op2
instance toString Expr
instance toString VarDecl
+instance toString FunDecl
instance zero Pos
instance == Op1