Re: proper use of add-function

[Noam Postavsky <npostavs@gmail.com>]

On 22 May 2018 at 18:58, Eric Abrahamsen <eric@ericabrahamsen.net> wrote:

> (add-function
>    :filter-args
>    (local 'canonically-space-region)
>    #'my-canonical-space-region)

You're adding to the function value in the (non-existent) buffer-local
variable `canonically-space-region'

canonically-space-region’s value is
#f(advice-wrapper :filter-args #f(compiled-function
(&rest args)
#<bytecode 0x15054ad>)
my-canonical-space-region)
Local in buffer *scratch*; globally void

You probably want advice-add instead:

(advice-add 'canonically-space-region
        :filter-args
        #'my-canonical-space-region)

Note: this affects canonically-space-region globally, so you have to
change the implementation of my-canonical-space-region so that it's a
nop except when operating in the relevant buffers.