How can I toggle between three predefined positions?

Question

I am trying to create an Emacs like Ctrl-l feature, similar to Vim's H, M and L. For those who don't now, these keys jump to top, middle, and bottom of the window. I already have something but I am missing the "if" part.

function! ToggleHML()
    let l:winheight = winheight('%')
    let l:top = 1
    let l:middle = l:winheight / 2
    let l:bottom = l:winheight
    if ...
endfunction

I think I have to create another variable to keep the state until the next function call, but I don't know how to.

Another thing I ended up thinking, exec a normal command inside the function. Something like:

:exec 'normal! H'

Answer 1

This should do what you're looking for:

function! ToggleHML()
    if winline() < winheight('%') / 2
      normal M
    elseif winline() < winheight('%')
      normal L
    else
      normal H
    endif
endfunction

I removed the variables, since they aren't really necessary. This will always jump down unless it's already at the bottom, in which case it will jump up.

Answer 2

After some sweat, I figured out one solution, not so easy as I thought. We have to discover if the file is larger or not than winheight('%').

function! ToggleHML()
    set scrolloff=0
    let l:last_win_line = ( line('$') <= winheight('%') ? line('$')  : winheight('%')  )
    if winline() < l:last_win_line / 2
      normal M
    elseif winline() < l:last_win_line
      normal L
    else
      normal H
    endif
endfunction
nnoremap <C-l> :call ToggleHML()<CR>

Reference: http://vim.1045645.n5.nabble.com/Vim-General-f1139531.html were I figured ou how to get the last line number line('$').