I want a calculator that lets me do instant calculation with low precision and then do the same calculation to higher precision, and that is instantly responsive.
I want to be able to mix values that are functions of time with simple scalars.
One aspect of this is using interval arithmetic or some similar kind of approximation to ensure that the rendering is responsive and doesn’t block user input.
Another aspect is that I want to see a time-series dangling from each non-scalar-valued operator and variable in my expression, although maybe not all of equal prominence; maybe mouseovers to focus on the active ones. And in some cases, I'd like to see it updating in real time as I'm editing the expression, like if it's a sound signal I'm generating.
I want the time axis to be vertical, rather than the usual horizontal, because the expression is traditionally represented horizontally, and trying to run the time axis horizontally too would mean that you can’t see much of any variable.
Another is that the RPN aspect of rpn-edit works really well: each keystroke has an immediate effect, and there are no unbalanced-parentheses errors. So I want to stick with that. If I'm playing music, I probably want the leftmost top-level value to be the one that's played by default, rather than the ones I'm building up to the right.
Another thing, though, is that I want to be able to move back and forth between continuous and discrete time-series without changing the formula, and I want to be able to apply the same function to different input time-series. This requires some kind of functional abstraction, at least giving names to things.
For trading analysis, I need more powerful time-series manipulation than what I’ve implemented so far. I need to be able to control, and in particular subset, time. I need to be able to conform time-series acquired with different (and irregular) time bases. I need operations on selections like “extend ten minutes into the future”. I need to be able to apply smoothing filters.