function! s:swap_lines(n1, n2)
 let line1 = getline(a:n1)
 let line2 = getline(a:n2)
 call setline(a:n1, line2)
 call setline(a:n2, line1)
endfunction
 
function! s:swap_up()
 let n = line('.')
 if n == 1
 return
 endif
 
 call s:swap_lines(n, n - 1)
 exec n - 1
endfunction
 
function! s:swap_down()
 let n = line('.')
 if n == line('$')
 return
 endif
 
 call s:swap_lines(n, n + 1)
 exec n + 1
endfunction
 
nmap <silent> <c-k> :call <SID>swap_up()<CR>
nmap <silent> <c-j> :call <SID>swap_down()<CR>
 
imap <silent> <c-k> :call <SID>swap_up()<CR>
imap <silent> <c-j> :call <SID>swap_down()<CR>