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...>]

I don't understand the problem.

Why would you expect *subst* to evaluate the variables *b* and *c *inside a
quoted expression?

         -s

On Sun, Oct 13, 2024 at 12:25 PM Eduardo Ochs <edu...@gm...> wrote:

> Hi list,
>
> these are my current notes on the semantics of makelist:
>
>
> --snip--snip--
> format([args]) :=
>   apply(?format, append([false], args));
>
> [a:b, b:c, c:d];             /* [b,c,d] */
> ['a, a, ''a, ''''a];         /* [a,b,c,d] */
> f1(o) ::= format("~a", o);   /*   just lispify */
> f2(o)  := format("~a", o);   /* ev and lispify */
>
> f1('a);                      /* ((MQUOTE SIMP) $A) */
> f1 (a);                      /* $A */
> f2('a);                      /* $A */
> f2 (a);                      /* $B */
>
> f1(2+3);                     /* 5 */
> f1(lambda([], 2+3));         /* ((LAMBDA SIMP) ((MLIST)) ((MPLUS) 2 3)) */
>
> 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]] */
>
> ev     ('[a,b,c],     a=42);       /* [42,c,d] */
> ev     ('[a,b,c],   ''a=42);       /* [b,42,d] */
> ev     ('[a,b,c], ''''a=42);       /* [b,c,42] */
>
> makelist([a,b,c],    'a, 42,43);   /* [[42,c,d], [43,c,d]] */
> makelist([a,b,c],   x+y, 42,43);   /* [[b,c,d], [b,c,d]] */
>
> ev('[a,b,c],     a=42);       /* [42,c,d] */
> ev('[a,b,c],    'a=42);       /* [42,c,d] */
> ev('[a,b,c],   x+y=42);       /* [b,c,d]  */
>
> sublis([x+y=42], '[a,b,c]);   /* err      */
> subst ([x+y=42], '[a,b,c]);   /*  [a,b,c] */
> subst ( '[a=42], '[a,b,c]);   /* [42,b,c] */
> subst ('['a=42], '[a,b,c]);   /*  [a,b,c] */
> --snip--snip--
>
>
> And here is just the bit that I don't understand, with less context:
>
>
> --snip--snip--
> [a:b, b:c, 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]] */
> ev     ('[a,b,c],  a=42);      /* [42,c,d] */
> ev     ('[a,b,c], 'a=42);      /* [42,c,d] */
> subst('[ a=42], '[a,b,c]);     /* [42,b,c] */
> subst('['a=42], '[a,b,c]);     /* [a,b,c] */
> --snip--snip--
>
>
> Note that:
> the quote in the "a" did not matter in the two "makelist"s above,
> the quote in the "a" did not matter in the two "ev"s above,
> the quote in the "a" _did_ matter in the two "subst"s above.
>
> So... all my attempts to translate the "ev"s above to "subst"s have
> failed miserably, my mental buffer has overflown, and I can't find a
> way to draw the orders of evaluation in a way that explains why the
> quotes on some "a"s don't matter... I _guess_ that I might be able to
> solve that after sleeping a lot, but I thought that the question was
> interesting enough, and worth asking...
>
> Btw, here is a too-short version of the question. Is there a
> straightforward way to translate the two "ev"s below to "subst"s?
> How? Note the "a=42" and the "'a=42"...
>
>   [a:b, b:c, c:d];
>   ev('[a,b,c],  a=42);      /* [42,c,d] */
>   ev('[a,b,c], 'a=42);      /* [42,c,d] */
>
>
> Cheers, and thanks in advance!
>   Eduardo Ochs
>   http://anggtwu.net/eev-maxima.html
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