[RFC]: add support for custom key bindings in the REPL

[Snehil-Shah]

Description

This RFC proposes adding support for custom key bindings in the REPL.

Some prior art:

• Julia: supports key bindings for actions like editing, cursor movement, and program control. Here's the full list of actions

• IPython: They also support multiple key bindings for a single action. Similar to how we have the right arrow and TAB to auto-complete a suggestion. They also have auto-closing pairs as "key bindings", to trigger the 'auto-close-parentheses' is mapped to the key (. Here's the full list of actions

We would also want to support having custom key bindings for current actions like Ctrl+O for inserting a new line, or right arrow for accepting a suggestion, or the TAB key to toggle the completions etc.

Would suggest reading the above lists of actions for further discussion on what we should support

Checklist

• [X] I have read and understood the Code of Conduct.
• [X] Searched for existing issues and pull requests.
• [X] The issue name begins with RFC:.

[kgryte]

Most of Julia's keybindings seem reasonable. IPython's are a little hard to follow; however, some of the autosuggestion bindings could be useful.

[Snehil-Shah]

Should we allow multiple keybindings for an action?

[kgryte]

Seems fine to me.

[Snehil-Shah]

Should we allow configuring basic actions like backspace and moving left/right (using arrow keys) which are implemented by readline? We would have to override the default readline behavior to make it configurable.

Update: Let's just make it configurable, instead of reimplementing the behavior, we can just "pipe" the new key binding to call the old key binding sequence.

[kgryte]

Whatever you think makes sense. My initial thought was that supporting overriding for those keybindings seems like a rabbit hole if it means overriding readline, but if you think you have a reasonable workaround, seems fine to me.

[Snehil-Shah]

Should I break it into separate PRs, namely:

• adding editor actions and keybinding support
• updating current actions to be configurable
• add settings and updating docs