Epsilon: Allow the user not to close parens, quotes etc.

[adriweb]

Set up:
In the calculation app, a user types 2 * ( 3 + 5 then presses [EXE].

Current situation:
The calculator tells the user that there is a syntax error.

Proposed situation:
The calculator ignores the missing closing _X_ character (in this case, _X_ being a parenthesis) and computes what the user intended: 2*(3+5), resulting in less time wasted.
To be clearer to the user, as soon as an open-_X_ character is typed, the OS would append the matching closing one to the current input, in a lighter color for instance.

Comments:

• This could work for characters like parens (for expressions), quotes (for strings), brackets (both curly and square, for lists and matrices).
• Support for nested characters would have to be done.
• ... and support for characters being deleted, too, where the inserted matching closed one would go away as well.
• Note: this is the way things work on some TI calculators (ignoring only on the z80/ez80, "grey draw" on the Nspire), and possibly others.

Example:

[Zezombye]

Also maybe add autocompletion support for commas. For example, if I select "sum" from the toolbox, it gives me sum(|,,), and if I type '6' then ',', it should override the present comma instead of adding another.

The Casio calculators also support missing closing brackets btw.

[yeKcim]

A pretty solution, could be colored brackets.

If there is only one brackets level, stay black. Each sublevel has its own color. If a bracket is open and not closed (or closed and not opened) it's red. Colors have to be used each time it's helpful…

A mockup (I thought "1st level stay black" after drawing)

[matheod]

I think it is better if student are forced to close bracket.
We already have too many student typing 1+x/2 instead of (1+x)/2 ...

If this sort of thing get ever added, I think it should be an option disabled by defaut.

But some coloring of bracket could be good (for exemple cooloring the "cursor touched" bracked couple).

[RubenNumworks]

Related to #587