table behaviour

[Mipps]

following roughly outlined lua file:

addonName = {}
addon.name = "..."
 
function addonName:foo()
   ...
end
 
function.OnAddOnLoaded()
   addonName:foo()
end
 
EVENT_MANAGER:RegisterForEvent(addon.name, EVENT_ADD_ON_LOADED, addon.OnAddOnLoaded)

(its a rough downgrade of one of the tutorials from the wiki...)

ingame I get following error message:

"function expected instead of nil"

what I don't understand: In the tutorial it worked but here not?