path: root/src/iflow.sml

(* Copyright (c) 2010, Adam Chlipala
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * - Redistributions of source code must retain the above copyright notice,
 *   this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright notice,
 *   this list of conditions and the following disclaimer in the documentation
 *   and/or other materials provided with the distribution.
 * - The names of contributors may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *)

structure Iflow :> IFLOW = struct

open Mono

structure IS = IntBinarySet
structure IM = IntBinaryMap

structure SS = BinarySetFn(struct
                           type ord_key = string
                           val compare = String.compare
                           end)

val writers = ["htmlifyInt_w",
               "htmlifyFloat_w",
               "htmlifyString_w",
               "htmlifyBool_w",
               "htmlifyTime_w",
               "attrifyInt_w",
               "attrifyFloat_w",
               "attrifyString_w",
               "attrifyChar_w",
               "urlifyInt_w",
               "urlifyFloat_w",
               "urlifyString_w",
               "urlifyBool_w"]

val writers = SS.addList (SS.empty, writers)

type lvar = int

datatype exp =
         Const of Prim.t
       | Var of int
       | Lvar of lvar
       | Func of string * exp list
       | Recd of (string * exp) list
       | Proj of exp * string
       | Finish

datatype reln =
         Known
       | Sql of string
       | Eq

datatype prop =
         True
       | False
       | Unknown
       | And of prop * prop
       | Or of prop * prop
       | Reln of reln * exp list
       | Select of int * lvar * lvar * prop * exp

local
    open Print
    val string = PD.string
in

fun p_exp e =
    case e of
        Const p => Prim.p_t p
      | Var n => string ("x" ^ Int.toString n)
      | Lvar n => string ("X" ^ Int.toString n)
      | Func (f, es) => box [string (f ^ "("),
                             p_list p_exp es,
                             string ")"]
      | Recd xes => box [string "{",
                         p_list (fn (x, e) => box [string "x",
                                                   space,
                                                   string "=",
                                                   space,
                                                   p_exp e]) xes,
                         string "}"]
      | Proj (e, x) => box [p_exp e,
                            string ("." ^ x)]
      | Finish => string "FINISH"

fun p_reln r es =
    case r of
        Known =>
        (case es of
             [e] => box [string "known(",
                         p_exp e,
                         string ")"]
           | _ => raise Fail "Iflow.p_reln: Known")
      | Sql s => box [string (s ^ "("),
                      p_list p_exp es,
                      string ")"]
      | Eq =>
        (case es of
             [e1, e2] => box [p_exp e1,
                              space,
                              string "=",
                              space,
                              p_exp e2]
           | _ => raise Fail "Iflow.p_reln: Eq")

fun p_prop p =
    case p of
        True => string "True"
      | False => string "False"
      | Unknown => string "??"
      | And (p1, p2) => box [string "(",
                             p_prop p1,
                             string ")",
                             space,
                             string "&&",
                             space,
                             string "(",
                             p_prop p2,
                             string ")"]
      | Or (p1, p2) => box [string "(",
                            p_prop p1,
                            string ")",
                            space,
                            string "||",
                            space,
                            string "(",
                            p_prop p2,
                            string ")"]
      | Reln (r, es) => p_reln r es
      | Select (n1, n2, n3, p, e) => box [string ("select(x" ^ Int.toString n1
                                                  ^ ",X" ^ Int.toString n2
                                                  ^ ",X" ^ Int.toString n3
                                                  ^ "){"),
                                          p_prop p,
                                          string "}{",
                                          p_exp e,
                                          string "}"]

end

local
    val count = ref 1
in
fun newLvar () =
    let
        val n = !count
    in
        count := n + 1;
        n
    end
end

fun subExp (v, lv) =
    let
        fun sub e =
            case e of
                Const _ => e
              | Var v' => if v' = v then Lvar lv else e
              | Lvar _ => e
              | Func (f, es) => Func (f, map sub es)
              | Recd xes => Recd (map (fn (x, e) => (x, sub e)) xes)
              | Proj (e, s) => Proj (sub e, s)
              | Finish => Finish
    in
        sub
    end

fun subProp (v, lv) =
    let
        fun sub p =
            case p of
                True => p
              | False => p
              | Unknown => p
              | And (p1, p2) => And (sub p1, sub p2)
              | Or (p1, p2) => Or (sub p1, sub p2)
              | Reln (r, es) => Reln (r, map (subExp (v, lv)) es)
              | Select (v1, lv1, lv2, p, e) => Select (v1, lv1, lv2, sub p, subExp (v, lv) e)
    in
        sub
    end

fun isKnown e =
    case e of
        Const _ => true
      | Func (_, es) => List.all isKnown es
      | Recd xes => List.all (isKnown o #2) xes
      | Proj (e, _) => isKnown e
      | _ => false

fun isFinish e =
    case e of
        Finish => true
      | _ => false

fun simplify e =
    case e of
        Const _ => e
      | Var _ => e
      | Lvar _ => e
      | Func (f, es) =>
        let
            val es = map simplify es
        in
            if List.exists isFinish es then
                Finish
            else
                Func (f, es)
        end
      | Recd xes =>
        let
            val xes = map (fn (x, e) => (x, simplify e)) xes
        in
            if List.exists (isFinish o #2) xes then
                Finish
            else
                Recd xes
        end
      | Proj (e, s) =>
        (case simplify e of
             Recd xes =>
             getOpt (ListUtil.search (fn (x, e') => if x = s then SOME e' else NONE) xes, Recd xes)
           | e' =>
             if isFinish e' then
                 Finish
             else
                 Proj (e', s))
      | Finish => Finish

fun decomp fals or =
    let
        fun decomp p k =
            case p of
                True => k []
              | False => fals
              | Unknown => k []
              | And (p1, p2) => 
                decomp p1 (fn ps1 =>
                              decomp p2 (fn ps2 =>
                                            k (ps1 @ ps2)))
              | Or (p1, p2) =>
                or (decomp p1 k, fn () => decomp p2 k)
              | Reln x => k [x]
              | Select _ => k []
    in
        decomp
    end

val unif = ref (IM.empty : exp IM.map)

fun reset () = unif := IM.empty
fun save () = !unif
fun restore x = unif := x

fun lvarIn lv =
    let
        fun lvi e =
            case e of
                Const _ => false
              | Var _ => false
              | Lvar lv' => lv' = lv
              | Func (_, es) => List.exists lvi es
              | Recd xes => List.exists (lvi o #2) xes
              | Proj (e, _) => lvi e
              | Finish => false
    in
        lvi
    end

fun eq' (e1, e2) =
    case (e1, e2) of
        (Const p1, Const p2) => Prim.equal (p1, p2)
      | (Var n1, Var n2) => n1 = n2

      | (Lvar n1, _) =>
        (case IM.find (!unif, n1) of
             SOME e1 => eq' (e1, e2)
           | NONE =>
             case e2 of
                 Lvar n2 =>
                 (case IM.find (!unif, n2) of
                      SOME e2 => eq' (e1, e2)
                    | NONE => n1 = n2
                              orelse (unif := IM.insert (!unif, n1, e2);
                                      true))
               | _ =>
                 if lvarIn n1 e2 then
                     false
                 else
                     (unif := IM.insert (!unif, n1, e2);
                      true))

      | (_, Lvar n2) =>
        (case IM.find (!unif, n2) of
             SOME e2 => eq' (e1, e2)
           | NONE =>
             if lvarIn n2 e1 then
                 false
             else
                 (unif := IM.insert (!unif, n2, e1);
                  true))
                                       
      | (Func (f1, es1), Func (f2, es2)) => f1 = f2 andalso ListPair.allEq eq' (es1, es2)
      | (Recd xes1, Recd xes2) => ListPair.allEq (fn ((x1, e1), (x2, e2)) => x1 = x2 andalso eq' (e1, e2)) (xes1, xes2)
      | (Proj (e1, s1), Proj (e2, s2)) => eq' (e1, e2) andalso s1 = s2
      | (Finish, Finish) => true
      | _ => false

fun eq (e1, e2) =
    let
        val saved = save ()
    in
        if eq' (simplify e1, simplify e2) then
            true
        else
            (restore saved;
             false)
    end

exception Imply of prop * prop

fun rimp ((r1, es1), (r2, es2)) =
    case (r1, r2) of
        (Sql r1', Sql r2') =>
        r1' = r2' andalso
        (case (es1, es2) of
             ([Recd xes1], [Recd xes2]) =>
             let
                 val saved = save ()
             in
                 if List.all (fn (f, e2) =>
                                 case ListUtil.search (fn (f', e1) => if f' = f then SOME e1 else NONE) xes1 of
                                     NONE => true
                                   | SOME e1 => eq (e1, e2)) xes2 then
                     true
                 else
                     (restore saved;
                      false)
             end
           | _ => false)
      | (Eq, Eq) =>
        (case (es1, es2) of
             ([x1, y1], [x2, y2]) =>
             let
                 val saved = save ()
             in
                 if eq (x1, x2) andalso eq (y1, y2) then
                     true
                 else
                     (restore saved;
                      (*raise Imply (Reln (Eq, es1), Reln (Eq, es2));*)
                      eq (x1, y2) andalso eq (y1, x2))
             end
           | _ => false)
      | (Known, Known) =>
        (case (es1, es2) of
             ([e1], [e2]) =>
             let
                 fun walk e2 =
                     eq (e1, e2) orelse
                     case e2 of
                         Proj (e2, _) => walk e2
                       | _ => false
             in
                 walk e2
             end
           | _ => false)
      | _ => false

fun imply (p1, p2) =
    (reset ();
     (*raise (Imply (p1, p2));*)
     decomp true (fn (e1, e2) => e1 andalso e2 ()) p1
            (fn hyps =>
                decomp false (fn (e1, e2) => e1 orelse e2 ()) p2
                (fn goals =>
                    let
                        fun gls goals onFail =
                            case goals of
                                [] => true
                              | g :: goals =>
                                let
                                    fun hps hyps =
                                        case hyps of
                                            [] => onFail ()
                                          | h :: hyps =>
                                            let
                                                val saved = save ()
                                            in
                                                if rimp (h, g) then
                                                    let
                                                        val changed = IM.numItems (!unif) <> IM.numItems saved
                                                    in
                                                        gls goals (fn () => (restore saved;
                                                                             changed andalso hps hyps))
                                                    end
                                                else
                                                    hps hyps
                                            end
                                in
                                    hps hyps
                                end
                    in
                        gls goals (fn () => false)
                    end)))


fun patCon pc =
    case pc of
        PConVar n => "C" ^ Int.toString n
      | PConFfi {mod = m, datatyp = d, con = c, ...} => m ^ "." ^ d ^ "." ^ c



datatype chunk =
         String of string
       | Exp of Mono.exp

fun chunkify e =
    case #1 e of
        EPrim (Prim.String s) => [String s]
      | EStrcat (e1, e2) =>
        let
            val chs1 = chunkify e1
            val chs2 = chunkify e2
        in
            case chs2 of
                String s2 :: chs2' =>
                (case List.last chs1 of
                     String s1 => List.take (chs1, length chs1 - 1) @ String (s1 ^ s2) :: chs2'
                   | _ => chs1 @ chs2)
              | _ => chs1 @ chs2
        end
      | _ => [Exp e]

type 'a parser = chunk list -> ('a * chunk list) option

fun always v chs = SOME (v, chs)

fun parse p s =
    case p (chunkify s) of
        SOME (v, []) => SOME v
      | _ => NONE

fun const s chs =
    case chs of
        String s' :: chs => if String.isPrefix s s' then
                                SOME ((), if size s = size s' then
                                              chs
                                          else
                                              String (String.extract (s', size s, NONE)) :: chs)
                            else
                                NONE
      | _ => NONE

fun follow p1 p2 chs =
    case p1 chs of
        NONE => NONE
      | SOME (v1, chs) =>
        case p2 chs of
            NONE => NONE
          | SOME (v2, chs) => SOME ((v1, v2), chs)

fun wrap p f chs =
    case p chs of
        NONE => NONE
      | SOME (v, chs) => SOME (f v, chs)

fun alt p1 p2 chs =
    case p1 chs of
        NONE => p2 chs
      | v => v

fun altL ps =
    case rev ps of
        [] => (fn _ => NONE)
      | p :: ps =>
        foldl (fn (p1, p2) => alt p1 p2) p ps

fun opt p chs =
    case p chs of
        NONE => SOME (NONE, chs)
      | SOME (v, chs) => SOME (SOME v, chs)

fun skip cp chs =
    case chs of
        String "" :: chs => skip cp chs
      | String s :: chs' => if cp (String.sub (s, 0)) then
                                skip cp (String (String.extract (s, 1, NONE)) :: chs')
                            else
                                SOME ((), chs)
      | _ => SOME ((), chs)

fun keep cp chs =
    case chs of
        String "" :: chs => keep cp chs
      | String s :: chs' =>
        let
            val (befor, after) = Substring.splitl cp (Substring.full s)
        in
            if Substring.isEmpty befor then
                NONE
            else
                SOME (Substring.string befor,
                      if Substring.isEmpty after then
                          chs'
                      else
                          String (Substring.string after) :: chs')
        end
      | _ => NONE

fun ws p = wrap (follow (skip (fn ch => ch = #" "))
                        (follow p (skip (fn ch => ch = #" ")))) (#1 o #2)

val debug = ref false

fun log name p chs =
    (if !debug then
         case chs of
             String s :: _ => print (name ^ ": " ^ s ^ "\n")
           | _ => print (name ^ ": blocked!\n")
     else
         ();
     p chs)

fun list p chs =
    altL [wrap (follow p (follow (ws (const ",")) (list p)))
               (fn (v, ((), ls)) => v :: ls),
          wrap (ws p) (fn v => [v]),
          always []] chs

val ident = keep (fn ch => Char.isAlphaNum ch orelse ch = #"_")

val t_ident = wrap ident (fn s => if String.isPrefix "T_" s then
                                      String.extract (s, 2, NONE)
                                  else
                                      raise Fail "Iflow: Bad table variable")
val uw_ident = wrap ident (fn s => if String.isPrefix "uw_" s then
                                       String.extract (s, 3, NONE)
                                   else
                                       raise Fail "Iflow: Bad uw_* variable")

val sitem = wrap (follow t_ident
                         (follow (const ".")
                                 uw_ident))
                 (fn (t, ((), f)) => (t, f))

datatype Rel =
         Exps of exp * exp -> prop
       | Props of prop * prop -> prop

datatype sqexp =
         SqConst of Prim.t
       | Field of string * string
       | Binop of Rel * sqexp * sqexp
       | SqKnown of sqexp
       | Inj of Mono.exp

val sqbrel = altL [wrap (const "=") (fn () => Exps (fn (e1, e2) => Reln (Eq, [e1, e2]))),
                   wrap (const "AND") (fn () => Props And),
                   wrap (const "OR") (fn () => Props Or)]

datatype ('a, 'b) sum = inl of 'a | inr of 'b

fun int chs =
    case chs of
        String s :: chs' =>
        let
            val (befor, after) = Substring.splitl Char.isDigit (Substring.full s)
        in
            if Substring.isEmpty befor then
                NONE
            else case Int64.fromString (Substring.string befor) of
                     NONE => NONE
                   | SOME n => SOME (n, if Substring.isEmpty after then
                                            chs'
                                        else
                                            String (Substring.string after) :: chs')
        end
      | _ => NONE

val prim = wrap (follow (wrap int Prim.Int) (opt (const "::int8"))) #1

fun known' chs =
    case chs of
        Exp (EFfi ("Basis", "sql_known"), _) :: chs => SOME ((), chs)
      | _ => NONE

fun sqlify chs =
    case chs of
        Exp (EFfiApp ("Basis", f, [e]), _) :: chs =>
        if String.isPrefix "sqlify" f then
            SOME (e, chs)
        else
            NONE
      | _ => NONE

fun sqexp chs =
    log "sqexp"
    (altL [wrap prim SqConst,
           wrap sitem Field,
           wrap known SqKnown,
           wrap sqlify Inj,
           wrap (follow (ws (const "("))
                        (follow (wrap
                                     (follow sqexp
                                             (alt
                                                  (wrap
                                                       (follow (ws sqbrel)
                                                               (ws sqexp))
                                                       inl)
                                                  (always (inr ()))))
                                     (fn (e1, sm) =>
                                         case sm of
                                             inl (bo, e2) => Binop (bo, e1, e2)
                                           | inr () => e1))
                                (const ")")))
                (fn ((), (e, ())) => e)])
    chs

and known chs = wrap (follow known' (follow (const "(") (follow sqexp (const ")"))))
                (fn ((), ((), (e, ()))) => e) chs

val select = log "select"
             (wrap (follow (const "SELECT ") (list sitem))
                   (fn ((), ls) => ls))

val fitem = wrap (follow uw_ident
                         (follow (const " AS ")
                                 t_ident))
                 (fn (t, ((), f)) => (t, f))

val from = log "from"
           (wrap (follow (const "FROM ") (list fitem))
                 (fn ((), ls) => ls))

val wher = wrap (follow (ws (const "WHERE ")) sqexp)
           (fn ((), ls) => ls)

val query = log "query"
                (wrap (follow (follow select from) (opt wher))
                      (fn ((fs, ts), wher) => {Select = fs, From = ts, Where = wher}))

fun queryProp env rv oe e =
    case parse query e of
        NONE => (print ("Warning: Information flow checker can't parse SQL query at "
                        ^ ErrorMsg.spanToString (#2 e) ^ "\n");
                 Unknown)
      | SOME r =>
        let
            val p =
                foldl (fn ((t, v), p) =>
                          And (p,
                               Reln (Sql t,
                                     [Recd (foldl (fn ((v', f), fs) =>
                                                      if v' = v then
                                                          (f, Proj (Proj (Lvar rv, v), f)) :: fs
                                                      else
                                                          fs) [] (#Select r))])))
                      True (#From r)

            fun expIn e =
                case e of
                    SqConst p => inl (Const p)
                  | Field (v, f) => inl (Proj (Proj (Lvar rv, v), f))
                  | Binop (bo, e1, e2) =>
                    inr (case (bo, expIn e1, expIn e2) of
                             (Exps f, inl e1, inl e2) => f (e1, e2)
                           | (Props f, inr p1, inr p2) => f (p1, p2)
                           | _ => Unknown)
                  | SqKnown e =>
                    inr (case expIn e of
                             inl e => Reln (Known, [e])
                           | _ => Unknown)
                  | Inj e =>
                    let
                        fun deinj (e, _) =
                            case e of
                                ERel n => List.nth (env, n)
                              | EField (e, f) => Proj (deinj e, f)
                              | _ => raise Fail "Iflow: non-variable injected into query"
                    in
                        inl (deinj e)
                    end

            val p = case #Where r of
                        NONE => p
                      | SOME e =>
                        case expIn e of
                            inr p' => And (p, p')
                          | _ => p
        in
            case oe of
                NONE => p
              | SOME oe =>
                And (p, foldl (fn ((v, f), p) =>
                                  Or (p,
                                      Reln (Eq, [oe, Proj (Proj (Lvar rv, v), f)])))
                              False (#Select r))
        end

fun evalExp env (e as (_, loc), st as (nv, p, sent)) =
    let
        fun default () =
            (Var nv, (nv+1, p, sent))

        fun addSent (p, e, sent) =
            if isKnown e then
                sent
            else
                (loc, e, p) :: sent
    in
        case #1 e of
            EPrim p => (Const p, st)
          | ERel n => (List.nth (env, n), st)
          | ENamed _ => default ()
          | ECon (_, pc, NONE) => (Func (patCon pc, []), st)
          | ECon (_, pc, SOME e) =>
            let
                val (e, st) = evalExp env (e, st)
            in
                (Func (patCon pc, [e]), st)
            end
          | ENone _ => (Func ("None", []), st)
          | ESome (_, e) =>
            let
                val (e, st) = evalExp env (e, st)
            in
                (Func ("Some", [e]), st)
            end
          | EFfi _ => default ()
          | EFfiApp (m, s, es) =>
            if m = "Basis" andalso SS.member (writers, s) then
                let
                    val (es, st) = ListUtil.foldlMap (evalExp env) st es
                in
                    (Func ("unit", []), (#1 st, p, foldl (fn (e, sent) => addSent (#2 st, e, sent)) sent es))
                end
            else if Settings.isEffectful (m, s) andalso not (Settings.isBenignEffectful (m, s)) then
                default ()
            else
                let
                    val (es, st) = ListUtil.foldlMap (evalExp env) st es
                in
                    (Func (m ^ "." ^ s, es), st)
                end
          | EApp _ => default ()
          | EAbs _ => default ()
          | EUnop (s, e1) =>
            let
                val (e1, st) = evalExp env (e1, st)
            in
                (Func (s, [e1]), st)
            end
          | EBinop (s, e1, e2) =>
            let
                val (e1, st) = evalExp env (e1, st)
                val (e2, st) = evalExp env (e2, st)
            in
                (Func (s, [e1, e2]), st)
            end
          | ERecord xets =>
            let
                val (xes, st) = ListUtil.foldlMap (fn ((x, e, _), st) =>
                                                      let
                                                          val (e, st) = evalExp env (e, st)
                                                      in
                                                          ((x, e), st)
                                                      end) st xets
            in
                (Recd xes, st)
            end
          | EField (e, s) =>
            let
                val (e, st) = evalExp env (e, st)
            in
                (Proj (e, s), st)
            end
          | ECase _ => default ()
          | EStrcat (e1, e2) =>
            let
                val (e1, st) = evalExp env (e1, st)
                val (e2, st) = evalExp env (e2, st)
            in
                (Func ("cat", [e1, e2]), st)
            end
          | EError _ => (Finish, st)
          | EReturnBlob {blob = b, mimeType = m, ...} =>
            let
                val (b, st) = evalExp env (b, st)
                val (m, st) = evalExp env (m, st)
            in
                (Finish, (#1 st, p, addSent (#2 st, b, addSent (#2 st, m, sent))))
            end
          | ERedirect (e, _) =>
            let
                val (e, st) = evalExp env (e, st)
            in
                (Finish, (#1 st, p, addSent (#2 st, e, sent)))
            end
          | EWrite e =>
            let
                val (e, st) = evalExp env (e, st)
            in
                (Func ("unit", []), (#1 st, p, addSent (#2 st, e, sent)))
            end
          | ESeq (e1, e2) =>
            let
                val (_, st) = evalExp env (e1, st)
            in
                evalExp env (e2, st)
            end
          | ELet (_, _, e1, e2) =>
            let
                val (e1, st) = evalExp env (e1, st)
            in
                evalExp (e1 :: env) (e2, st)
            end
          | EClosure (n, es) =>
            let
                val (es, st) = ListUtil.foldlMap (evalExp env) st es
            in
                (Func ("Cl" ^ Int.toString n, es), st)
            end

          | EQuery {query = q, body = b, initial = i, ...} =>
            let
                val (_, st) = evalExp env (q, st)
                val (i, st) = evalExp env (i, st)

                val r = #1 st
                val acc = #1 st + 1
                val st' = (#1 st + 2, #2 st, #3 st)

                val (b, st') = evalExp (Var acc :: Var r :: env) (b, st')

                val r' = newLvar ()
                val acc' = newLvar ()
                val qp = queryProp env r' NONE q

                val doSubExp = subExp (r, r') o subExp (acc, acc')
                val doSubProp = subProp (r, r') o subProp (acc, acc')

                val p = doSubProp (#2 st')
                val p = And (p, qp)
                val p = Select (r, r', acc', p, doSubExp b)
            in
                (Var r, (#1 st + 1, And (#2 st, p), map (fn (loc, e, p) => (loc,
                                                                            doSubExp e,
                                                                            And (qp, doSubProp p))) (#3 st')))
            end
          | EDml _ => default ()
          | ENextval _ => default ()
          | ESetval _ => default ()

          | EUnurlify _ => default ()
          | EJavaScript _ => default ()
          | ESignalReturn _ => default ()
          | ESignalBind _ => default ()
          | ESignalSource _ => default ()
          | EServerCall _ => default ()
          | ERecv _ => default ()
          | ESleep _ => default ()
          | ESpawn _ => default ()
    end

fun check file =
    let
        val exptd = foldl (fn ((d, _), exptd) =>
                              case d of
                                  DExport (_, _, n, _, _, _) => IS.add (exptd, n)
                                | _ => exptd) IS.empty file

        fun decl ((d, _), (vals, pols)) =
            case d of
                DVal (_, n, _, e, _) =>
                let
                    val isExptd = IS.member (exptd, n)

                    fun deAbs (e, env, nv, p) =
                        case #1 e of
                            EAbs (_, _, _, e) => deAbs (e, Var nv :: env, nv + 1,
                                                        if isExptd then
                                                            And (p, Reln (Known, [Var nv]))
                                                        else
                                                            p)
                          | _ => (e, env, nv, p)

                    val (e, env, nv, p) = deAbs (e, [], 1, True)

                    val (e, (_, p, sent)) = evalExp env (e, (nv, p, []))
                in
                    (sent @ vals, pols)
                end

              | DPolicy (PolQuery e) => (vals, queryProp [] 0 (SOME (Var 0)) e :: pols)

              | _ => (vals, pols)

        val () = reset ()

        val (vals, pols) = foldl decl ([], []) file
    in
        app (fn (loc, e, p) =>
                let
                    val p = And (p, Reln (Eq, [Var 0, e]))
                in
                    if List.exists (fn pol => imply (p, pol)) pols then
                        ()
                    else
                        (ErrorMsg.errorAt loc "The information flow policy may be violated here.";
                         Print.preface ("The state satisifes this predicate:", p_prop p))
                end) vals
    end

end