gistfile1.txt

" Completion menu: completes based on text of current file, as well as other
" open buffers/windows. Use <Tab> to open the menu (or pick another key, see
" the last line), as well as to cycle between the different options. Use
" <Enter> or <Space> to use use option.
set complete=.,w,b
set completeopt=longest,menu,menuone,preview
function! AutoCompleteOnKey(key)
  if pumvisible()      " menu open, loop through choices
    return "\<Down>"
  else                 " menu not open, open conditionally
    if strpart(getline('.'), 0, col('.') - 1) =~ '^\s*$'
      return a:key
    else
      return "\<C-N>\<C-R>=pumvisible() ? \"\\<Down>\" : \"\"\<CR>"
    end
  end
endfunction
inoremap <silent> <expr> <CR>    pumvisible() ? "\<C-y>"  : "\<C-g>u\<CR>"
inoremap <silent> <expr> <Space> pumvisible() ? "\<C-y> " : "\<Space>"
inoremap <silent> <expr> <Tab>   AutoCompleteOnKey("\<Tab>")