interactive expressions

[aberrantian]

When solving longer expressions on paper, one can break down the expressions into smaller sub-expressions, solve those, and then substitute it back into the root expression and repeat to solve the whole expression rather than try to solve the whole thing simultaneously.

On a monitor you don't have that luxury and users are forced to solve longer expressions simultaneously.

If the expression was interactive in such a way where the user could click or navigate via keyboard to a sub-expression and then focus on that then that would relieve some stress for the user.

[aberrantian]

The different steps should visually stack on one another so that the user can scroll and see the previous steps and the root expression.

There's another matter regarding this: should the user be allowed to input incorrect values before submitting and then told they were incorrect after submitting or should their input be rejected if it is incorrect while they are typing it? Or auto submit if they input is correct?