///replaceLink(from, toOld, toNew)
/**
 * replaceLink :: TypeConLink -> TypeConLink -> TypeConLink -> ()
 * 
 * Replaces an edge between one type con and another with a new target.
 *
 * @param from the source of the edge
 * @param toOld the current target of the edge
 * @param toNew the new target of the edge
 */

var from = argument0;
var toOld = argument1;
var toNew = argument2;

assertInstanceof(from, TypeConLink);
assertInstanceof(toOld, TypeConLink);
assertInstanceof(toNew, TypeConLink);

assert(toOld != toNew, "Replacing link from "+getInstObjName(from)+" to "+getInstObjName(toOld)+" by itself.");

ds_list_replace(from.to, ds_list_find_index(from.to, toOld), toNew);
if (ds_list_find_index(from.to, toOld) == -1)
  ds_set_delete(toOld.from, from);
ds_set_add(toNew.from, from);