How to fold lines are not interested in?

orttm.vim

function! s:Oritatami(pat)
  redir => ilist
  execute ':silent! global/' . a:pat . '/:echo line(".")'
  redir END

  let lnums = map(split(ilist, '\n'), 'str2nr(v:val)')
  if empty(lnums)
    echomsg printf('pattern "%s" is not found.', a:pat)
    return
  endif

  if lnums[0] != 1
    call insert(lnums, 1)
  endif
  if lnums[-1] != line('$')
    call add(lnums, line('$') + 1)
  endif

  for i in range(0, len(lnums) - 1)
    let start = get(lnums, i) + 1
    let end = get(lnums, i + 1)
    if end && start != end
      execute printf('%d,%dfold', start, end - 1)
    endif
  endfor
endfunction
command! -nargs=1 Orttm call s:Oritatami(<q-args>)