incorrect spacing in REPL for combining characters

[stevengj]

If you type e.g. \alpha<TAB>\hat<TAB>, it makes α̂. However, on my machine (MacOS) it displays an extra space after the character, which weirdly disappears when you hit <RETURN> or <TAB>.

cc: @loladiro

[aelg]

Also doing julia> \hat<TAB> puts the ^ on the > in the prompt.

[stevengj]

@aelg, \hat generates a Unicode combining character, which applies the hat to the previous character. So it isn't going to work quite like LaTeX (which applies the hat to the subsequent character).

[Keno]

We could probably put some kind of noncombining separator after the prompt though to prevent that from happening.

[aelg]

@stevengj No I understand that, I just thought it was worth mentioning, as it's probably not what anyone would want. It seems related enough, to the bug you reported, to mention it here instead of creating a new issue.

[Keno]

What should the behavior for navigating across combining characters be?
Some options:

1. Do the same thing as now and just fix the display. This would mean that a|^ and a^| (where ^ indicates combining hat and | indicates cursor position) look the same.
2. Step over the combined character.
3. Do something more fancy such as splitting the combining characters when the cursor is in between them.

[JeffBezanson]

Option 1 sounds good.

[stevengj]

Option 2 sounds better to me. (But I'd still like to have to hit twice to delete the combined character, so that I can delete just the decoration.) But option 1 should be fine for now.

Note that utf8proc will identify graphemes for you, if you want to move the cursor in units of graphemes.

[carlobaldassi]

FWIW in vim the behaviour is option 2. I don't know about other editors but it should be easy to test now that all of them implement latex substitution.

[Keno]

I've been using option 1 for the past 5 minutes and I hate it, so I'll try option 2 now.

[Keno]

Any by that I mean just navigation. Deletion will still delete the combining character.