As has been said above creating your own little language is probably not a very good idea. But isn't Matlab(tm) or Octave exactly what you need? It gives you loads of numerical functionality, has all the exits and error checking, provides easy data loading, has a GUI (at least recent matlab does; all chemists I know prefer GUI over code, don't ask me why ;-). You could try GNU octave first for free to check whether it fits your needs and then get some (expensive!) matlab licenses.
I hope I really got the point in your post...
you begin bashing the string with a +42 regexp of confusion