Re: Declaring Lisp function types

[Adam Porter <adam@alphapapa.net>]

>> That looks nice to me.  My only suggestion would be to change the symbol 
>> `function` to `type`, i.e.
>> 
>>    (defun sum (a b)
>>      (declare (type (integer integer) integer))
>>      (+ a b))
>> 
>> Because it would be more concise and descriptive.
> 
> FWIW, Andrea's proposal looks more descriptive to me.  "Type" is too
> general, whereas "function" is more specific.

I don't understand what you mean.  ISTM that "type" is exactly what's 
being declared; "function" would seem redundant, because it's already 
within a defun form, and less accurate, because it's not declaring the 
function itself but its types.

Another consideration is that using `(declare (function ...))` would 
preclude allowing `declare-function` forms to be moved into the 
`declare` form.

In fact, in Ement.el, I've already implemented this, please see:

https://github.com/alphapapa/ement.el/blob/2b9725accdaed1913b83b2495d3f901ee3aba892/ement-lib.el#L67-L89

Which is used like:

https://github.com/alphapapa/ement.el/blob/2b9725accdaed1913b83b2495d3f901ee3aba892/ement-notifications.el#L55

The advantage of allowing `declare-function` to be done as `(declare 
(function ...))` within a defun form is that it keeps the declaration 
with the function that makes it necessary, so if the defun is moved to 
another location, the declaration goes with it; and that then makes it 
easier to remove the declaration later if it becomes unnecessary.  (And, 
IMHO it looks cleaner than having declare-function forms littering a file.)

As you can see, I have a TODO item to propose this upstream, but I 
hadn't gotten around to it yet.  After having had it in "production" for 
some time without any reported problems, and seeing this thread, now 
seems like an appropriate time to propose it.  :)