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Re: map-put! and (setf (map-elt ...) ..) on lists

From: Nicolas Petton
Subject: Re: map-put! and (setf (map-elt ...) ..) on lists
Date: Mon, 17 Dec 2018 12:38:04 +0100

Stefan Monnier <address@hidden> writes:

Hi Stefan,

> The current handling of map-put on lists is very ad-hoc:
> The gv-expander of `map-elt` tests if the arg is a list and if so
> delegates to `alist-get`.
> It kind of works, but for a library that's supposed to be generic and
> expandable to other map types, this is undesirable.
> So in the patch below I change this such that `map-elt` does not special
> case lists any more.  Instead `map-put!` is changed to signal a special
> error when it can't do its job, and the gv-expander of `map-elt` catches
> this error and delegates the job to a new non-side-effecting
> `map-insert`.
> With this, we can add new map types via defmethod that work like lists
> (i.e. that don't support inplace update but can still be modified via
> `setf`).

I think it's a good step forward, thank you.

I'd like to start thinking about adding support for plists in map.el.


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