Unicode Input

[sharkdp]

Julia has a great feature where you can input Unicode characters using LaTeX-like abbreviations. This would be great for Numbats REPLs as well. We could type \pi<tab> to get π or \hbar to get ħ.

Open questions:

• It's probably fine to have a list of hard-coded sequences for this. Or should this be fully user-customizable? If so, which (new) construct should introduce those assignments?

[eminence]

I took a quick look at this, and this doesn't seem as trivial as it might initially seem: rustyline doesn't seem to handle tab completions when the completion (like π) isn't a prefix of the input (like \pi).

Relevant issue: kkawakam/rustyline#593

[Bzero]

If it is too hard to do tab completions I think a reasonable alternative could be to allow LaTeX math abbreviations in the REPL input which are not replaced interactively while entering them but which are replaced in a step before passing the input to the actual numbat compiler.

[sharkdp]

I took a quick look at this, and this doesn't seem as trivial as it might initially seem: rustyline doesn't seem to handle tab completions when the completion (like π) isn't a prefix of the input (like \pi).

It looks like it did support that at some point, because kalker is based on (an old version of) rustyline and it allows you to type sqrt<tab> and it will be replaced by √. Their code is here. I tried something similar using code like this:

diff --git a/numbat-cli/src/completer.rs b/numbat-cli/src/completer.rs
index 572bc55..6746ee8 100644
--- a/numbat-cli/src/completer.rs
+++ b/numbat-cli/src/completer.rs
@@ -20,6 +20,16 @@ impl Completer for NumbatCompleter {
         pos: usize,
         _: &rustyline::Context<'_>,
     ) -> rustyline::Result<(usize, Vec<Self::Candidate>)> {
+        if line[..pos].ends_with("\\hbar") {
+            return Ok((
+                pos - "\\hbar".len(),
+                vec![Pair {
+                    display: "ℏ".into(),
+                    replacement: "ℏ".into(),
+                }],
+            ));
+        }
+
         if line.starts_with("use ") {
             return Ok((
                 0,

but it does not work as expected. Maybe this is a regression in rustyline? Unicode characters also seem to be handled incorrectly, because replacing e.g. h<tab> with ℏ works, but replacing h<tab> with x does not work — only with something longer. So they probably call "ℏ".len() instead of "ℏ".unicode_width() somewhere.

[sharkdp]

Oh — it works with CompletionType::Circular! But not with CompletionType::List, which is what we currently use in Numbat.

Upstream ticket: kkawakam/rustyline#748