Live result preview in the interactive session

[JohannesWeinbrecht]

I love using numbat as a fast, keyboard based calculator in the terminal.
For this, I use the interactive session.

To make this use case more comfortable, it would be great to have a live evaluation of the expression, as a preview, while typing.
I think it would be possible to implement this using an inline viewport from ratatui.
More concretely, my idea of the live preview would be to just show the same text or error as the interactive session would show after pressing ENTER.

Maybe a little mandatory delay between the last keystroke and the evaluation would be needed for the preview not being annoying. Otherwise, errors could be showing due to incomplete expressions whilst still typing.

Implementing this depends on #736, but as stated there, the Monaco Editor PR #741 already does some kind of live evaluation.
The goal would just be to bring this live evaluation into the interactive terminal session.

[sharkdp]

Thank you for your feature request.

We have various "frontends" for Numbat. The new mobile interface actually has live preview: #218 (comment)

The interface is currently optimized for mobile, but you can actually also use the app on desktops.

[sharkdp]

More to your point: implementing this in the CLI would be a major rework, yes. There are quite a few readline features that we depend on, so I'm not sure if rebuilding everything with ratatui would be feasible?

[JohannesWeinbrecht]

Feasibility depends on the developer, I guess. When I created the issue, I played around with it a bit. I came to the same conclusion as you do: It would take a lot of work because the current code relies a lot on readline features. Also, from what I found, there isn't any ratatui widget crate out there that truly fits this use case.

I think one should also look into keeping the readline prompt and just using a ratatui inline viewport below it.
I don't know for a certain if it's possible, but it would spare a lot of work.

Lastly, I think we should still keep this issue. I think it would be cool to have the live preview in the cli/tui and if someone chooses to do the ratatui rework, it would also open the door to a much nicer looking, "real" TUI.
Sadly, my rust proficiency is not up to the level to do this myself in the near future, but in the little time I have currently I will keep tinkering around with this while learning rust (but if anyone else is up for it, please feel free!).