How do I make the h key go to prev tab if at start of file?

Question

And, to get back again: how do I make the l key go to next tab, if at end of file?

I'd also like to make hh go to previous buffer, and ll go to next buffer. I know that'll add a delay to recognising the h/l keys, and slow down navigation, and I wonder is there a way to tell vim to

Only check for "hh" at start of file, and only check for "ll" at end of file

Answer 1

Like Ben and statox, I wouldn't necessarily recommend this, but it is possible:

function FirstPress(c1) abort
  let now = reltime()
  while reltimefloat(reltime(now)) < &timeoutlen / 1000.0
    " See if the user has typed another character
    let c2 = getchar(0)

    if c2 != 0
      " The user typed something. Was it another h?
      if c2 == char2nr(a:c1)
        " The user typed a double h, switch buffers
        if a:c1 == 'h'
          bprevious
        else
          bnext
        endif
      else
        " The user typed something else. Switch tabs and replay what they typed
        call feedkeys((a:c1 == 'h' ? 'gT' : 'gt') . nr2char(c2), 't')
      endif
      return
    endif
  endwhile

  " The user didn't press anything. Switch Tabs
  if a:c1 == 'h'
    tabprevious
  else
    tabnext
  endif
endfunction

nnoremap <expr> h (getpos('.')[1] == 1 && getpos('.')[2] == 1) ? ':call FirstPress("h")<CR>' : 'h'
nnoremap <expr> l (getpos('.')[1] == line('$') && (getpos('.')[2] == col('$') - 1 \|\| col('$') == 1)) ? ':call FirstPress("l")<CR>' : 'l'

It works by mapping the single h and l keypresses only, and then in that mapping, checking if the user presses the given key a second time, and acting accordingly.

See also my answer to this recent similar, but slightly different question where the OP wanted to do the first mapping immediately and then perform the second as well if performed within timeoutlen.

Answer 2

how do I make the l key go to next tab, if at end of file

For this part make a function which checks that the following two conditions are satisfied:

1. The value of line("."), which is the current line number, and line("$"), which is the number of all lines in a file, match
2. The current column value, obtained with col("."), and the length of the current line, obtained with strlen(getline(".")), match.

This means that you're on the last line, on the last column (i.e. the last character in the file).

I hope this pushes you in the right direction.