/*
 * Consequence.js v 0.2.0
 * 
 * * * * * *
 * LICENSE
 * 
 * The MIT License
 * 
 * Copyright (c) 2011 Sean E. Dunn
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 * 
 * * * * * *
 * OVERVIEW
 * 
 * Consequence.js is a Javascript library for reactive programming:
 * http://en.wikipedia.org/wiki/Reactive_programming
 * 
 * With Consequence.js, one can set a state clause that, when satisfied at any 
 * time, results in the execution of bound imperative handlers, for either the 
 * positive (true) case, or the negative (false) case.
 * 
 * This library can be used when a programmer would rather say "whenever some 
 * complex state set X happens, do Y, and let me not worry about when", instead
 * of "whenever I can, check whether some complex state set X is happening and 
 * do Y". Example domains where this could be useful are games, user
 * interfaces, and, to give an example where this exists presently, in 
 * spreadsheets.
 * 
 * * * * * *
 * IN DETAIL
 * 
 * In the traditional imperitive model, it is the responsibility of the 
 * programmer to write constructs that regularly check whether state has been 
 * satisfied in order to execute subsequent instructions. In the Consequence.js 
 * reactive programming model, a binding is made between the state clause which 
 * must be satisfied at some point in the future, and the code which handles 
 * the positive and negative results of that state.
 * 
 * Consequence.js provides a simple binding for describing what variables are
 * being watched, what test determines the trigger condition, and what to
 * execute if the test is true or false.
 *
 * E.g.,
 * 
 *   // Set variables
 *   var a = new Cq(0, 0, 1);
 *   var b = new Cq("apple");
 * 
 *   // Define binding
 *   var binding = CqBind([a,b], function(){ return a.v==1 && b.v=="apple"; },
 *      function() {
 *          // state satisfied, do something. This is the affirmative handler, 
 *          // which is required.
 *          window.alert("State satisfied!");
 *      }, function() {
 *          // state not satisfied, do nothing. This is the negative handler, 
 *          // which is optional.
 *      });
 *
 *   // Satisfy the state, causing the window the pop up.
 *   a.v = 1;
 * 
 *   // Cleanup
 *   binding.unbind();
 *  
 *   ////////////////
 *   
 * Variables are created by newing a Cq object set to a value. The value may 
 * be of any type. The Cq constructor takes two optional arguments; a min 
 * value, and a max value. If set, all values outside this inclusive range are 
 * ignored, and will not trigger handlers. To use them, the value must support 
 * > and < operations.
 * 
 * The internal connection of the Cq object to the handlers happens via CqBind.
 * CqBind takes two mandatory arguments and two arguments that may be undefined.
 * It returns a binding which may be destroyed by calling unbind() on it.
 * 
 *   CqBind(varList, testFunc, trueFunc, falseFunc)
 * 
 * varList is an array of operators for which the binding should watch for 
 * changes within. If something interesting happens to these variables,
 * testFunc is called. If it returns true, then trueFunc is called. If it 
 * returns false, the falseFunc is called. To call neither, return undefined.
 * 
 * Within the testFunc, there are four special methods which tell you more
 * about the context of your test. <var>.set() tells you if this test is
 * being called because <var> was set. <var>.changed() works the same way,
 * but is true if the variable was modified. <var>.last() tells you what
 * the last value was. The fourth is this.last(), which tells you what this
 * test function returned the last time it was called. This is useful for
 * instances where you'd like to make sure trueFunc/falseFunc are only called
 * when the test value changes, for example.
 * 
 * * * *
 * API
 * 
 * OBJECTS
 * 
 * Cq
 * Constructor
 *      Cq(value, min=undefined, max=undefined):
 *          To create a variable that can be used in a state clause, create a Cq 
 *          object using new.     
 *          value: initial value of object
 *          min: optional minimum value object can be set to
 *          max: optional maximum value object can be set to 
 * Members
 *      v: use to set/get value of Cq object
 * Methods
 *      set90: For use in the test function. Returns true if the test function
 *          was called because this variable was set.
 *      changed(): For use in the test function. Returns true if the test function
 *          was called because this variable was modified.
 *      last(): For use in the test function. Returns the last value of this 
 *          variable before the current value.
 * 
 * CqBinding
 * Methods
 *      last(): For use in the test function, accessed by calling this.last(). 
 *          Returns the value last returned by this function.
 *      unbind(): Destroy this binding.
 *      
 * CqSet
 * Constructor
 *      CqSet():
 *          Default empty CqSet. A CqSet is a convenience object for organizing
 *          bindings and cleaning them up quickly.
 * Members
 *      insert(binding): Insert a binding.
 *      remove(binding): Remove a binding.
 *      unbind(): Unbind all bindings contained within this CqSet.
 *
 * FUNCTIONS
 * 
 * CqBind(varList, testFunc, trueFunc, falseFunc): Return a new CqBinding.
 *     varList: Array of Cq variable objects.
 *     testFunc: Test that involves the varList variables. Return true to run
 *         the trueFunc, false for the falseFunc, and undefined for neither.
 *     trueFunc: If testFunc returns true, this is run.
 *     falseFunc: If testFunc returns false, this is run.
 * 
 */