before and after methods

Pascal Costanza pc at
Thu May 18 08:52:20 UTC 2017

> On 18 May 2017, at 10:42, Didier Verna <didier at> wrote:
> zbyszek <zbyszek at> wrote:
>> Dnia 2017-05-17, śro o godzinie 15:24 -0400, Sam Steingold pisze:
>>> If you are defining the method combination, you have way more freedom
>>> and flexibility than mere before and after.  Basically, you can do it
>>> yourself.
>> But Didier is asking about BUILT-IN method combinations.  Possibly it
>> was hard to define reasonable agreed semantics for before an after
>> methods in the case of something like AND or APPEND (technical
>> troubles aside).
>  Right. I was merely curious. It's pretty obvious to me why you
> wouldn't allow CALL-NEXT-METHOD in non-standard built-in combinations,
> but I can't figure out why or how before and after methods could be
> problematic, so I was wondering...

I’m just guessing, but one reason I can think of is that almost all of the built-in method combinations (except for standard and progn) are applicative. before/after methods don’t have a direct impact on the return value of a generic function call, so their primary purpose is to allow for specifying side effects, which presumably doesn’t make a lot of sense for applicative combinators.

Does that make any sense?


Pascal Costanza
The views expressed in this email are my own, and not those of my employer.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <>

More information about the pro mailing list