src/eval.sml

   1 (* HCoop Domtool (http://hcoop.sourceforge.net/)
   2  * Copyright (c) 2006, Adam Chlipala
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License
   6  * as published by the Free Software Foundation; either version 2
   7  * of the License, or (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
  17  *)
  18
  19 (* Execution of Domtool programs reduced to primitive actions *)
  20
  21 structure Eval :> EVAL = struct
  22
  23 open Ast
  24
  25 structure SM = StringMap
  26
  27 fun lookup (evs, ev) =
  28     case SM.find (evs, ev) of
  29         NONE => raise Fail ("Couldn't find an environment variable "
  30                             ^ ev ^ " that type-checking has guaranteed")
  31       | SOME v => v
  32
  33 fun printEvs (name, evs) =
  34     (print ("Environment " ^ name ^ "\n");
  35      SM.appi (fn (name, i) => Print.preface (name, Print.p_exp i)) evs;
  36      print "\n")
  37
  38 val conjoin : Env.env_vars * Env.env_vars -> Env.env_vars =
  39   SM.unionWith #2
  40
  41 fun findPrimitive e =
  42     let
  43         fun findPrim (e, _) =
  44             case e of
  45                 EVar name => (name, [])
  46               | EApp (e1, e2) =>
  47                 let
  48                     val (name, args) = findPrim e1
  49                 in
  50                     (name, e2 :: args)
  51                 end
  52               | _ => raise Fail "Non-primitive action left after reduction"
  53
  54         val (name, args) = findPrim e
  55     in
  56         (name, rev args)
  57     end
  58
  59 fun exec' evs (eAll as (e, _)) =
  60     case e of
  61         ESkip => SM.empty
  62       | ESet (ev, e) => SM.insert (SM.empty, ev, e)
  63       | EGet (x, _, ev, e) =>
  64         let
  65             val e' = Reduce.subst x (lookup (evs, ev)) e
  66         in
  67             exec' evs (Reduce.reduceExp Env.empty e')
  68         end
  69       | ESeq es =>
  70         let
  71             val (new, _) =
  72                 foldl (fn (e, (new, keep)) =>
  73                           let
  74                               val new' = exec' keep e
  75                           in
  76                               (conjoin (new, new'),
  77                                conjoin (keep, new'))
  78                           end) (SM.empty, evs) es
  79         in
  80             new
  81         end
  82       | ELocal (e1, e2) =>
  83         let
  84             val evs' = exec' evs e1
  85         in
  86             exec' (conjoin (evs, evs')) e2
  87         end
  88       | EWith (e1, e2) =>
  89         let
  90             val (prim, args) = findPrimitive e1
  91         in
  92             case Env.container prim of
  93                 NONE => raise Fail "Unbound primitive container"
  94               | SOME (action, cleanup) =>
  95                 let
  96                     val evs' = action (evs, args)
  97                     val evs'' = exec' evs e2
  98                 in
  99                     cleanup ();
 100                     evs'
 101                 end
 102         end
 103
 104       | _ =>
 105         let
 106             val (prim, args) = findPrimitive eAll
 107         in
 108             case Env.action prim of
 109                 NONE => raise Fail "Unbound primitive action"
 110               | SOME action => action (evs, List.map (Reduce.reduceExp Env.empty) args)
 111         end
 112
 113 fun exec evs e =
 114     let
 115         val _ = Env.pre ()
 116         val evs' = exec' evs e
 117     in
 118         Env.post ()
 119     end
 120
 121 end