type pos = int * int
type symbol = Symbol.t

type var = 
  | SimpleVar of symbol * pos
  | FieldVar of var * symbol * pos
  | SubscriptVar of var * exp * pos

and exp = 
  | VarExp of var
  | NilExp
  | IntExp of int
  | StringExp of string * pos
  | CallExp of symbol * exp list * pos
  | OpExp of exp * oper * exp * pos
  | RecordExp of (symbol * exp * pos) list * symbol * pos
  | SeqExp of exp list
  | AssignExp of var * exp * pos
  | IfExp of exp * exp *  exp option * pos
  | WhileExp of exp * exp * pos
	| ForExp of symbol * bool ref * exp *  exp * exp * pos
  | BreakExp of pos
  | LetExp of dec list * exp * pos
  | ArrayExp of symbol * exp * exp * pos

and dec = 
  | FunctionDec of fundec list
  | VarDec of vardec
  | TypeDec of tydec list

and ty =
  | NameTy of symbol * pos
  | RecordTy of field list
  | ArrayTy of symbol * pos

and oper = 
  | PlusOp 
  | MinusOp 
  | TimesOp 
  | DivideOp
  | EqOp 
  | NeqOp 
  | LtOp 
  | LeOp 
  | GtOp 
  | GeOp

and field = symbol * bool ref * symbol * pos

and fundec = symbol * field list * (symbol * pos) option * exp * pos

and tydec = (symbol * ty * pos)

and vardec = symbol * bool ref * (symbol * pos) option * exp * pos