Re: [Maxima-discuss] How do I translate the "ev" in "[a:b,b:c,c:d]; ev('[a,b,c],'a=42); " to a "subst"?

[Stavros M. <mac...@gm...>]

Internally *makelist* calls *ev*, but I've got to say that that shocks me
even more than the fact that *ev* has bizarre behavior itself. In
particular, I find this ridiculous:

makelist(['(x), '('x),'('('x))],'x,17,17) => [[17, '17, '('17)]]

Re using *'x* as a variable in *ev* and *makelist*, I doubt that the
implementers considered that case. It should probably raise an error.

Also, I don't know what you're trying to investigate by testing with *''a* and
*''''a*. That syntax is evaluated at *read, *so those are precisely
equivalent to *b* and *c*.

          -s


On Sun, Oct 13, 2024 at 7:00 PM Eduardo Ochs <edu...@gm...> wrote:

> On Sun, 13 Oct 2024 at 18:24, Stavros Macrakis <mac...@gm...> wrote:
>
>> To elaborate a bit on what Robert said, I strongly discourage you from
>> using *ev *programmatically if there is some other way to accomplish
>> what you want.
>>
>
>
>
> Hi all,
>
> I only tried to use ev because the documentation of makelist -
> from here:
>
>   (info "(maxima)makelist")
>   https://maxima.sourceforge.io/docs/manual/maxima_21.html#makelist
>
> says this:
>
>   The most general form, 'makelist (<expr>, <i>, <i_0>, <i_max>,
>   <step>)', returns the list of elements obtained when 'ev (<expr>,
>   <i>=<j>)' is applied to the elements <j> of the sequence: <i_0>,
>   <i_0> + <step>, <i_0> + 2*<step>, ..., with <|j|> less than or
>   equal to <|i_max|>.
>
> and that gave me the impression that it was standard, or at least
> common, to use ev to explain the semantics of special forms... but I
> find ev very confusing - and I only tried to understand ev because
> I tried this,
>
>   [a:'b, b:'c, c:'d];                /* [b,c,d] */
>   ['a, a, ''a, ''''a];               /* [a,b,c,d] */
>   makelist([a,b,c],    'a, 42,43);   /* [[42,c,d], [43,c,d]] */
>   makelist([a,b,c],     a, 42,43);   /* [[42,c,d], [43,c,d]] */
>   makelist([a,b,c],   ''a, 42,43);   /* [[b,42,d], [b,43,d]] */
>   makelist([a,b,c], ''''a, 42,43);   /* [[b,c,42], [b,c,43]] */
>
> and I found the result of the first makelist very surprising.
>
> Anyway: now I have many more things in my to-do list... I need to
> finish some experiments with Sly/Slime (urgent), understand the last
> messages by Robert and Stavros (urgent), and learn how to use trace
> (not urgent). =/
>
>   Cheers, thanks, etc...
>     Eduardo
>
>