local inter = CreateFrame("Frame", "Interruptor", UIParent)

function inter:UNIT_SPELLCAST_START(event, unitID, spell, rank, lineID, spellID)
     print"Spell cast start for " .. spell);
end

inter:SetScript("OnEvent",
                    function(self, event, ...)
                            if self[event] then
                                    return self[event] (self, event, ...)
                            end
                    end)
inter:RegisterEvent("UNIT_SPELLCAST_START")