local send_keys = function(str)
    return vim.api.nvim_replace_termcodes( str, true, true, true )
end

_G.arrow_down = function()
    return vim.fn.pumvisible() == 1 and send_keys "<C-n>" or send_keys "<down>"
end


_G.arrow_up = function()
    return vim.fn.pumvisible() == 1 and send_keys "<C-p>" or send_keys "<up>"
end 

map( 'i', '<up>',   'v:lua.arrow_up()',   { expr = true, silent = true }  )
map( 'i', '<down>', 'v:lua.arrow_down()', { expr = true, silent = true }  )