(* field-def.sml
 *
 * COPYRIGHT (c) 2010 The Diderot Project (http://diderot.cs.uchicago.edu)
 * All rights reserved.
 *)

structure FieldDef =
  struct

  (* the static definition of a field value *)
    datatype field_def =
      = CONV of ImageInfo.info * Kernel.kernel	(* convolution *)
      | DIFF of int * field_def			(* k levels of differentiation *)
      | NEG of field_def
      | SUM of field_def * field_def
(* scaling too? *)

  (* normalize a field definition by pushing the DIFF operators to the
   * leaves
   *)
    fun normalize fld = let
	  fun norm fld = (case fld
		 of CONV _ => fld
		  | DIFF(k, fld) => diff (k, fld)
		  | NEG fld => NEG(norm fld)
		  | SUM(fld1, fld2) => SUM(norm fld1, norm fld2)
		(* end case *))
	  and diff (k, fld) = (case fld
		 of CONV _ => DIFF(k, fld)
		  | DIFF(k', fld) => diff (k+k', fld)
		  | NEG fld => NEG(diff(k, fld))
		  | SUM(fld1, fld2) => SUM(diff(k, fld1), diff(k, fld2))
		(* end case *))
	  in
	    norm fld
	  end

  end