Vim/Lua - exporting balloon info as Lua data and running external script to create the balloon text

extBalloonLuaScript.vim

set balloonexpr=Balloon()
let g:BalloonScript="<scriptname>"
set ballooneval

function! Balloon()
   let balloondata = ['return', '{']
   call add(balloondata, "  ['cwd']         = [[" . getcwd()        . "]],")
   call add(balloondata, "  ['fileabspath'] = [[" . expand('%:p')   . "]],")
   call add(balloondata, "  ['filerelpath'] = [[" . expand('%:.')   . "]],")
   call add(balloondata, "  ['fileabsdir']  = [[" . expand('%:p:h') . "]],")
   call add(balloondata, "  ['filereldir']  = [[" . expand('%:.:h') . "]],")
   call add(balloondata, "  ['file']        = [[" . expand('%:t')   . "]],")
   call add(balloondata, "  ['filename']    = [[" . expand('%:t:r') . "]],")
   call add(balloondata, "  ['fileext']     = [[" . expand('%:e')   . "]],")
   call add(balloondata, "  ['line']        = [[" . v:beval_lnum    . "]],")
   call add(balloondata, "  ['column']      = [[" . v:beval_col     . "]],")
   call add(balloondata, "  ['text']        = [[" . v:beval_text    . "]],")
   call add(balloondata, "}")
   call writefile(balloondata, "/path/to/.vimballooninfo")
   call system(g:BalloonScript)
   return join(readfile("/path/to/.vimballoontext"), "\n")
endfunction

" to load the data into a Lua script run
" t = dofile("/path/to/.vimballooninfo")
" the Lua script shall write the balloon text into the file "/path/to/.vimballoontext".