how to make keybind with lua?

as example

local sampev = require 'samp.events'

function waitUntilSampAvailable()

while not isSampAvailable() do

wait(0)

end

end

function main()

waitUntilSampAvailable()

end

function sampev.onServerMessage(colour, msg)

lua_thread.create(function()

if string.find(msg, "halo") then

sampSendChat("/pm a")

end

end)

end

raksamp show some error

please help me