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

[Nicolas Petton]

Drew Adams <address@hidden> writes:

> Do we have a non-destructive `map-put'?

There's `map-insert'.

> I see that there is a macro `map-put', so I guess that would qualify.
> But no - that macro is now obsolete - replaced by `map-put!'.
>
> Much more important than the function name, however, is
> the real answer: Put the important info in the doc string.

The docstring, yes, of course, but the function name is IMHO the most
important part of the documentation.

> That's what should have been done at the outset, and
> AFAICT it still hasn't been done, here.  I see these doc
> strings for the obsolete `map-put' and the new `map-put!',
> respectively:
>
> map-put:
>
>  Associate KEY with VALUE in MAP and return VALUE.
>  If KEY is already present in MAP, replace the associated value
>  with VALUE.
>  When MAP is a list, test equality with TESTFN if non-nil, otherwise use 
> `eql'.
>
>  MAP can be a list, hash-table or array.
>
> map-put!:
>
>  Associate KEY with VALUE in MAP and return VALUE.
>  If KEY is already present in MAP, replace the associated value
>  with VALUE.
>
> The only change was to get rid of the last two lines (the
> first of which is too long, BTW).
>
> Whoa!  Nothing anywhere there that says whether a copy is
> returned or the original value is mutated.  That's a bug,
> IMO.

Agreed.  I'll fix that.

> If you really want clarity about whether a function is
> destructive, put it in the doc string.  That's the real
> answer to Stefan's quandary, "Don't use "!" as a suffix"
> doesn't say what to do instead."
>
> That's the place to start.  And unless there is also to
> be a non-destructive version, and we _need_ to have two
> different names, there is no need to have any name
> indication that a given function is "destructive".

As I said, I like Stefan's approach, but if everybody else dislike it,
and if you think it's not idiomatic Elisp, then let's change the name.

Stefan, would it be ok with you?

Cheers,
Nico

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