(* util.sml
 *
 * Utility code for Simplification.
 *
 * This code is part of the Diderot Project (http://diderot-language.cs.uchicago.edu)
 *
 * COPYRIGHT (c) 2015 The University of Chicago
 * All rights reserved.
 *)

structure Util : sig

  (* return information about a reduction operator *)
    val reductionInfo : Var.t -> {
	    rator : Var.t,			(* primitive operator *)
	    init : Literal.t,			(* identity element to use for initialization *)
	    mvs : SimpleTypes.meta_arg list	(* meta-variable arguments for primitive application *)
	  }

  end = struct

    structure BV = BasisVars
    structure L = Literal
    structure R = RealLit

    fun reductionInfo rator =
	  if Var.same(BV.red_all, rator)
	    then {rator = BV.op_and, init = L.Bool true, mvs = []}
	  else if Var.same(BV.red_exists, rator)
	    then {rator = BV.op_or, init = L.Bool false, mvs = []}
	  else if Var.same(BV.red_max, rator)
	    then {rator = BV.fn_max, init = L.Real R.negInf, mvs = []}
	  else if Var.same(BV.red_mean, rator)
	    then raise Fail "FIXME: 'mean' reduction not yet supported"
	  else if Var.same(BV.red_min, rator)
	    then {rator = BV.fn_min, init = L.Real R.posInf, mvs = []}
	  else if Var.same(BV.red_product, rator)
	    then {rator = BV.mul_rr, init = L.Real R.one, mvs = []}
	  else if Var.same(BV.red_sum, rator)
	    then {rator = BV.add_tt, init = L.Real R.one, mvs = [SimpleTypes.SHAPE[]]}
	  else if Var.same(BV.red_variance, rator)
	    then raise Fail "FIXME: 'variance' reduction not yet supported"
	    else raise Fail(Var.uniqueNameOf rator ^ " is not a reduction operator")

  end