Suggestion for tab-completion alternative

[JohnScholes]

I like the unobtrusive way the bash shell does tab-completion. In particular:

• PopUp appears only on request (Tab Tab), so no PopUp delay timeout needed.
• Handles single-match without having to select it by keying an additional Tab.

• Tab navigates among common prefixes with few keystrokes:

  Select the last item from:
  xxx_aaa_yyy
  xxx_bbb_ccc
  xxx_bbb_aaa
  
  x  →  x
  Tab  →  xxx_
  b  →  xxx_b
  Tab  →  xxx_bbb_
  a  →  xxx_bbb_a
  Tab  →  xxx_bbb_aaa

  Repeat:                                          ⍝ input line
      Select char ← input                          ⍝ char from keyboard
      Case Tab:                                    ⍝ tab-completion:
          list ← possible suffix strings           ⍝ possible completions
          Select ≢list                             ⍝ number of list items:
          Case 0: insert blanks                    ⍝ 0:regular tabbing
          Case 1: buffer ,← ⍞←,list                ⍝ 1:take single option
          Else:                                    ⍝ several options:
              pref ← common prefix of list items   ⍝ (may be empty)
              buffer ,← ⍞←pref                     ⍝ echo common prefix 
              Select char ← input                  ⍝ next char
              Case Tab:                            ⍝ 2nd Tab: show choices
                  choice ← select from POPUP       ⍝ pop up choices 
                  buffer ,← ⍞← suffix from choice  ⍝ complete choice 
              Else: buffer ,← ⍞←char               ⍝ echo & accumulate
      Else: buffer ,← ⍞←char                       ⍝ echo & accumulate
  Until char=Enter                                 ⍝ end of line

  Modulo bugs in my above code, this is effectively a 2-state machine with the outer Case Tab: hosting a "Tab received" state.

• Regular tabbing just-works as expected (insert blanks up to next tab-stop). Getting a tab-completion when you just wanted some blanks is easily avoided (start with an initial blank) or corrected (Undo).
• Failing to find an expected match will append 1-4 blanks, which are easily undone.

[e9gille]

I think we could get this to work even in combination with the current completion wizard.

[JohnScholes]

If we implement this, a question arises: should we append a '.' when tab-completing a space name? The bash shell appends a gratuitous terminator (/) to tab-completed directory names. However, many shell commands, such as cd(1) are happy to ignore such terminators when they're not required, so they don't in general cause a problem. The same is not true with superfluous dots after namespaces in Dyalog and so, on balance, I suggest not appending the dot would be less confusing/irritating, even though removing an unwanted one with a single Backspace keystroke would be easy.

[e9gille]

@JohnScholes try the latest master. I changed the option for Autocomplete to allow selecting "shell" style.

Let me know what you think.

[JohnScholes]

This now feels very good Gil. Thanks.

[e9gille]

My pleasure.