When you use callsub or callfunc, this command allows you to go back to the
calling script. You can optionally return with a value telling the calling
program what exactly happened. To get at this value, you will have to use the
'set' command:

set <variable>,callfunc "<your function>"

Note the round brackets. Turns out you have to enclose just about anything in
brackets if it isn't a straight number for the return command to work with it:

return (@x+@y);

Also note that

if (<condition>) return (<whatever>);

does NOT always work, even though it would make scripts a lot cleaner, and it
might be wiser to avoid using it like that.

For an example see 'callfunc' and 'callsub'