dyalog-apl-input is an Emacs input method that uses the default RIDE key mappings for the en_US locale. The `-key (backquote) is used as the prefix for the key sequence.
It can simply be loaded with a (require) (assuming it is in the load-path) like so:
(push "~/.emacs.d/lisp" load-path)
(require 'dyalog-apl-input)
C-h I describes the input method.