structure Elab =
struct
  fun primop (s : string) : Syntax.primop =
    case s of
      "exit" => Syntax.PExit
    | _ => raise Fail ("invalid op: " ^ s)

  fun elaborate (p : Syntax.expr) : Syntax.lexp =
    case p of
      Syntax.EIdent [i] => raise Fail "only primitive operations for now, no variables"
    | Syntax.EIdent _ => raise Fail "long identifiers are not supported"
    | Syntax.EBuiltin builtin => Syntax.LPrim (primop builtin)
    | Syntax.EInt i => Syntax.LInt i
    | Syntax.EStr s => Syntax.LString s
    | Syntax.ETuple exprs => Syntax.LRecord (map elaborate exprs)
    | Syntax.EList exprs =>
        foldr
          (fn (x, acc) =>
            Syntax.LRecord [elaborate x, acc])
          (Syntax.LInt 0)
          exprs
    | Syntax.EApp (f, x) => Syntax.LApp (elaborate f, elaborate x)
    | Syntax.ETyped (e, _) => elaborate e
    | Syntax.EAndAlso (_, _) => raise Fail "unimplemented"
    | Syntax.EOrElse (_, _) => raise Fail "unimplemented"
    | Syntax.ELet (decls, body) =>
        Syntax.LRecord
          (map elaborate
            (map (fn (Syntax.DVal e) => e) decls @ [body]))
    | Syntax.ELambda e => Syntax.LFn (Gensym.new (), elaborate e)
end