Add if..then..else

[hcoop/domtool2.git] / src / eval.sml

(* HCoop Domtool (http://hcoop.sourceforge.net/)
 * Copyright (c) 2006, Adam Chlipala
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 *)

(* Execution of Domtool programs reduced to primitive actions *)

structure Eval :> EVAL = struct

open Ast

structure SM = StringMap

fun lookup (evs, ev) =
    case SM.find (evs, ev) of
	NONE => raise Fail ("Couldn't find an environment variable "
			    ^ ev ^ " that type-checking has guaranteed")
      | SOME v => v

fun printEvs (name, evs) =
    (print ("Environment " ^ name ^ "\n");
     SM.appi (fn (name, i) => Print.preface (name, Print.p_exp i)) evs;
     print "\n")

val conjoin : Env.env_vars * Env.env_vars -> Env.env_vars =
  SM.unionWith #2

fun findPrimitive e =
    let
	fun findPrim (e, _) =
	    case e of
		EVar name => (name, [])
	      | EApp (e1, e2) =>
		let
		    val (name, args) = findPrim e1
		in
		    (name, e2 :: args)
		end
	      | _ => raise Fail "Non-primitive action left after reduction"

	val (name, args) = findPrim e
    in
	(name, rev args)
    end

fun exec' evs (eAll as (e, _)) =
    case e of
	ESkip => SM.empty
      | ESet (ev, e) => SM.insert (SM.empty, ev, e)
      | EGet (x, _, ev, e) => exec' evs (Reduce.subst x (lookup (evs, ev)) e)
      | ESeq es =>
	let
	    val (new, _) =
		foldl (fn (e, (new, keep)) =>
			  let
			      val new' = exec' keep e
			  in
			      (conjoin (new, new'),
			       conjoin (keep, new'))
			  end) (SM.empty, evs) es
	in
	    new
	end
      | ELocal (e1, e2) =>
	let
	    val evs' = exec' evs e1
	in
	    exec' (conjoin (evs, evs')) e2
	end
      | EWith (e1, e2) =>
	let
	    val (prim, args) = findPrimitive e1
	in
	    case Env.container prim of
		NONE => raise Fail "Unbound primitive container"
	      | SOME (action, cleanup) =>
		let
		    val evs' = action (evs, args)
		    val evs'' = exec' evs e2
		in
		    cleanup ();
		    evs'
		end
	end

      | _ =>
	let
	    val (prim, args) = findPrimitive eAll
	in
	    case Env.action prim of
		NONE => raise Fail "Unbound primitive action"
	      | SOME action => action (evs, List.map (Reduce.reduceExp Env.empty) args)
	end

fun exec evs e =
    let
	val _ = Env.pre ()
	val evs' = exec' evs e
    in
	Env.post ()
    end

end