2.2 構文解析

exception Error of string
let err s = raise (Error s)

type id = string

type binOp = Plus | Mult | Lt

type exp =
    Var       of id
  | ILit      of int
  | BLit      of bool
  | BinOp     of binOp * exp * exp
  | IfExp     of exp * exp * exp
  | LetExp    of id * exp * exp
  | FunExp    of id * exp
  | AppExp    of exp * exp
  | LetRecExp of id * id * exp * exp
  | LoopExp   of id * exp * exp (* loop <id> = <exp> in <exp> *)
  | RecurExp  of exp            (* recur <exp> *)
  | TupleExp  of exp * exp      (* (<exp>, <exp>) *)
  | ProjExp   of exp * int      (* <exp> . <int> *)