Set::Infinite TODO 

- include "backtrack_callback" in the parameter list for _function() 

- document the "separators" method - use example from t/infinite.t
  Find out how to make it more user friendly.

- quantize() should use "iterate"
  (unless this breaks _quantize_span)
  Find out how to unify "quantize" and the "_recurrence" module (DT::Set)

- spaceship should return "undef" if the sets can't be compared.
- "contains" should test the result of "==" for undef.
- count() should return "undef" if the set can't be counted.

- test new methods

- methods:
  is_infinite
  exists( sub ) / any / ...

- Deprecate min_a()
  min() should check "wantarray", instead.
  This can generate confusion in some cases - verify this.

- New methods: map / grep
  From a discussion with Andrew Pimlott and Dave Rolsky
  Find out how to implement "block" syntax 
  (" {} " instead of " sub{} ") -- use '&' prototype
  - test under 5.005_03
  
  update: It looks like this is not possible:
  http://www.perlmonks.org/index.pl?node_id=312978
  from perlsub:
  "Pretty much the exclusive domain of prototypes is to 
  make a perl sub act like a builtin. Once you call it 
  via $subref-> or &subname, you are no longer treating 
  it as a builtin and prototypes are ignored."

- Redo POD
- difference between "size" and "count"

- Change syntax: from Class::method to Class->method

Old TODO:

    - parser (another module)

    - _quantize_span should only be used inside backtrack()
      Implementing quantize() using iterator() should make 
      _quantize_span() unnecessary.

    - provide a constructor that allow for un-ordered and overlapping spans

    - verify and fix unbalanced trace_open/trace_close 

    - move (offset, quantize), or most of Arithmetic.pm, to Date::Set 
    - refactor "widgets" out of the main code. Maybe create
      a Set::Infinite::Widgets directory (offset, quantize).
    - give more standard names to Arithmetic.pm variables
    - implement "last of quantize"

    - remove _quantize_span()

    - a set with first == inf or last = -inf is an error!

    - tests for "iterate" min/max/first/last
      These may fail if "iterate" returns >= 2 elements
    - more tests for min/max/span/size on too_complex sets

    - find out how to compare "<=>" unbounded sets
    - try using first() in intersects() and "<=>"
    - test finding out min/max of integer open sets (see backtrack.t tests 2,3)

    - fix _todo/bigfloat, _todo/bigint

BACKTRACK

    backtrack.t:

	test backtrack on:
		iterate -- returning more than 1 element
		compact
                tolerance
                complement

	backtracking: implement remaining tests in backtrack.t
	verify results in backtrack.t

    backtracking: document backtracking resolution

SYNTAX

	extra: Make a 'strict' option for "quantize" and other filters, 
	that will intersect
	each unit back to the object, that is:
	Interval:                     [************************]
	Quantized:                [*********)[*********)[*********)
	Quantized->Stricted:          [*****)[*********)[******]

	think about: "push-pop", "dup", "drop" mechanism

	think about: some "if-else" mechanism

DOCUMENTATION

	check: POD formatting and contents 

	verify, document parameter syntax everywhere

	document:
		??? offset option 'mode=>circle'
		new method 'list'
		iterate

        document as "internal":
                min_a
                max_a
                backtrack
	        trace

	??? document: quantize extensibility through hash-subs

CACHEING

	cache quantize by month/day/...
	-- doesn't work if 'quant' is changed
	-- doesn't check 'intersects'
	make a 'flush'-cache method. Make a 'cache-registry'.
	think about: caching for union, etc