Dumb little RPN calculator, learning project for CS 193P, taught by Paul 
Hegarty.  Don't try to use for anything useful.  Not well tested.

For more info, see http://cs193p.stanford.edu/

- Sef Kloninger


TODO

- I now getting these warnings from the Operator class.
  "PerformSelector may cause a leak because its selector is unknown"
- Not sure if saving/loading defaults is actually working.  How to
  test? Debugger seems to get confused
- When we don't have the right number of operands, consider going
  into an "error mode" and displaying a red "E" or something like 
  that.  Now it just assumes zero and runs with that, which is a 
  little presumptuous.
- Same with divide-by-zero case.  Currently just evals to zero.
  Infinity makes more sense, error makes even more sense.


Icon courtesy of PSD Graphics (http://www.psdgraphics.com/), free for non-commercial 
use.  Thanks guys!


Profiling data, iPad, complicated function with lots of panning and pinching:

Running      Time    Self        Symbol Name
7178.0ms   34.8%    7178.0      -[GraphView drawLineBetweenPointA:andB:inContext:]
3751.0ms   18.1%    3751.0      +[CalculatorBrain popAndEvaluate:usingVariableDict:]
1639.0ms    7.9%    1639.0      -[Operator evaluateOperand:withOperand:]
1341.0ms    6.5%    1341.0      +[CalculatorBrain isOperator:]
1186.0ms    5.7%    1186.0      +[CalculatorBrain runProgram:usingVariableDict:]
891.0ms      4.3%    891.0      +[Operator operatorFromOpname:]