Sure, it might be useful, but I don't think you want to avoid
error-checking for *anything* that is accessible from the Maxima user
level.
On Tue, Sep 8, 2009 at 1:07 PM, Richard Fateman<fateman at cs.berkeley.edu> wrote:
> I think that it might be useful to have a $pushS and a $popS in lisp that
> worked solely on global lisp symbols like L which were
> bound to expressions of the form? L =? ((mlist simp)? a b c ....)? if there
> is a time-critical application.
>
> where pushS(d, L)?? made L into?? ((mlist simp) $d a b c ...)
> and??? popS(L)???????? made L into?? ((mlist simp a b c) and returned $d
>
> It would also be easy to write.
> Now the question is:? should pushS and popS do all the checking needed to
> validate the assumptions and if they are not valid, do "the other stuff"?
>
> How can we check that L is a global lisp symbol, anyway?
>
> RJF
>
>
> Stavros Macrakis wrote:
>
> On Tue, Sep 8, 2009 at 9:59 AM, ?iga Lenar?i?<ziga.lenarcic at gmail.com>
> wrote:
>
>
> On Sep 8, 2009, at 3:22 PM, Stavros Macrakis wrote:
>
>
> It is an error to use Lisp's push function to modify a Maxima
> variable. In particular, this means you can't push onto a subscripted
> variable: zz[1]:[]$ push(3,zz[1]) => error.
>
>
> Ah, these are the cases I always forget about, because accessing a maxima
> variable that is also a lisp variable is so easy to do. So in this case I
> can get the attached list with 'meval', modify it, but how do I then attach
> it back to the zz[1]?
>
>
> Good question. Another interesting question is whether the push
> variable should be evaluated twice. Consider:
>
> push( 3, x[i:i+1] )
>
> Surely you don't want this to be equivalent to
>
> x[i:i+1] : cons(3, x[i:i+1])
>
> which assigns to a different array location than the one from which it
> reads, but rather something like
>
> ( temp: (i:i+1), x[temp]: cons(3, x[temp] ) )
>
> This sort of mess is perhaps one reason that push is not part of the
> standard Maxima core.
>
>
>
> One way is probably by constructing a 'mset' expression and evaluating it,
> but can we use something cheaper in this case (since it is known what we
> want)?
>
>
> Why would you construct an mset expression? There is already an mset
> function in mlisp.lisp.
>
>
>
> To make a fast push/pop I would still have special code, when push/pop gets
> a 'symbolp' (regular Maxima variable). In this case it's probably OK to just
> use lisp's 'set'?
>
>
> This is a bad idea for two reasons: 1) it makes your code unnecessary
> complicated; 2) it duplicates the same functionality in two places.
> The second is the really crucial point. If at some point the
> semantics of mset change (e.g. because we change scoping rules or
> whatever), how will the maintainer know that he/she should also change
> your push/pop functions? And are they really that slow?
>
> -s
>
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