How to call an anonymous function from a Frame in a WoW addon?

Question

I'm using a code generator that emits many anonymous functions. I thought I'd try calling one from a Frame, but it doesn't seem to work; I get:

Date: 2020-09-18 18:42:27
ID: 1
Error occured in: Global
Count: 1
Message: [string "HelloWorldFrame:OnLoad"] line 1:
   attempt to call global 'HelloWorld' (a nil value)
Debug:
   [C]: HelloWorld()
   [string "*:OnLoad"]:1:
      [string "*:OnLoad"]:1

If I change the following:

local HelloWorld = function()
  print("Hello, World!");
end

to:

function HelloWorld() 
  print("Hello, World!"); 
end

it will work.

Here's my XML:

<Ui xmlns="http://www.blizzard.com/wow/ui/" 
                   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
                   xsi:schemaLocation="http://www.blizzard.com/wow/ui/ 
                   ..\..\FrameXML\UI.xsd">
  <Frame name="HelloWorldFrame">
   <Scripts>
    <OnLoad>
     HelloWorld();
    </OnLoad>
   </Scripts>
  </Frame>
</Ui>

Is this possible?

Answer 1

The short answer is you need to use globals if you use XML. Something like this

Lua

MyUniqueAddon = {}

function MyUniqueAddon:HelloWorld()
    print("Hello, World!"); 
end

XML

<Frame name="HelloWorldFrame">
    <Scripts>
        <OnLoad>
            MyUniqueAddon:HelloWorld();
        </OnLoad>
    </Scripts>
</Frame>

You can also just do everything in Lua

local function OnEvent(self, event)
    print("Hello, World!"); 
end

local f = CreateFrame("Frame")
f:RegisterEvent("PLAYER_ENTERING_WORLD")
f:SetScript("OnEvent", OnEvent)

Or in this case not use a frame at all if you just want to print something as an exercise

print("Hello, World!");