On the help emacs list Stefan made some elisp suggestions for the apl mode.
Since its about nitty-gritties of elisp I think this may be the more
suitable list.

So heres some code to input apl. (attached)
Currently there is no major-mode stuff.
Just in any mode if you run this (and you have a scroll-lock key
working) then scroll-lock behaves like a toggle for an apl keyboard.
[If scroll-lock is not there as on laptops, you will need to pick some
other key and change that line]

If there is something fundamentally wrong with this line please let me know