Calca - Humane Symbolic Calculator for OS X and iOS

One feature that Soulver has that I would love to see in Calca is combinatorics - you can do x choose y in Soulver.

Calca takes ideas from Soulver and super sizes them:

* Soulver allows free text editing within a line of computation; Calca allows free editing in the entire file

* Both update as you type

* Soulver understands arithmetic; Calca knows algebra, calculus, and algorithms

* Soulver requires that all variables be defined; Calca does not

* Soulver does not support user defined functions; to Calca, everything is a function

* Soulver has no programming constructs; Calca is one step away from being a general purpose programming language.

* Soulver does not support matrices; Calca does

Have you seen the IPython Notebook?

http://ipython.org/notebook.html

I think it does what you want

It's from scratch C# code using Xamarin to build the UI layers for iOS/OS X. Well, I also use a parser generator jayc which is based on jay which is a yacc cc. Everything else is mine. It's a pretty standard Expression tree implementation with a symbolic interpreter.