Why do I need to have my functions written first in my PowerShell script?

Remember that in general, what works in a script should work at the command line.

This was not true in CMD. GOTO and FOR %I IN (...) DO %%I are two examples.

In PowerShell, I can run commands at the command line until I get the result I want, then paste the history in to a script, then edit out the extraneous bits.

Also, I can take a script that isn’t working correctly, paste it in to an interactive shell, and study the resulting state.

At the interactive command line, there’s no way you could write this:

F
function F { "Hello, World!" }

However, when reading a script, I want to read the top-level code first, and then see more detail as I scroll down. One approach is:

function Main 
{
    F
}

function F
{
    "Hello, World!"
}

Main