type binop    = Add | Sub | Mul | Div
type monop  = UnaryMinus
type promise={d:(data ref) option; ex:expr; gamma: env}
and data =
  | Numeric of expr array (*num[n1,...nm]*)
  | String of expr array(*str[s1,...sm]*)
  | Gen of (data ref) array (*gen[nu1...num]*)
  | Closure of f list * expr * env (*\f1..\fn.e,G*)
  | PromiseD of promise
and u=
  | Value of data
  | Promise of promise
and expr =
  | Num of float (*n*)
  | Str of string (*s*)
  | Symbol of string
  | ArrayAccess of expr * expr (*x[[e]]*)
  | CompoundExpression of expr * expr  (*{e;e}*)
  | FunctionDeclaration of f list * expr (*function(f1,..fn) e*)
  | Application of expr * a list (*x(a1,...an)*)
  | AssignExpression of expr * expr (*x<-e*)
  | ArrayAssignWithIndex of expr * expr * expr (*x[e]<-e*)
  | U of u ref (*u*)
  | PartialEvaluation of (data ref) * (a list) (*nu(a1,..an)*)
(*  | BinOp  of binop * expr * expr
  | MonOp of monop * expr*)
and f=
  | Identifier of string
  | AssignParam of string * expr
and a=
  | Expr of expr
  | AssignArg of string * expr
and frameElement=
  | PromiseF of promise
  | DataRef of (data ref)

and frame = (expr, frameElement) Hashtbl.t
and env= (frame ref) list