cond, elseif, case... it doesn't really matter, as they can all be used to
do much the same thing. But whatever is chosen, it should be implemented in
Maxima's own language, for the many bozos like myself who don't want to have
to bother with the underlying language of whatever CAS they are using (C,
C++, Lisp, etc). Besides which, I have no especial love for lisp.
-Alasdair
On 1/8/07, Richard Fateman <fateman at cs.berkeley.edu> wrote:
>
> The cond statement in lisp is really very handy, and I find it far more
> useful than elseif, and indeed more useful than if-then-else which I use
> only if I can see immediately that the decision process is very simple.
> Lisp has all of these.
>
>
>
> You would write
>
> (cond ((= a b) a)
>
> ((< a b) (- b a))
>
> (t b))
>
>
>
> With the program attached, you could use this, in maxima:
>
> infix("->", 40,40);
>
> cond ( a=b ->a,
>
> a<b -> b-a,
>
> t -> b)
>
>
>
> With case and cond, many programs manipulating expressions can be written
> this way
>
>
>
> F(expr):= cond( atom(expr) ->dosomething(expr),
>
> T -> case(op(expr),
>
> "+" ->dosomethingsumrelated(expr),
>
> "*" ->
> dosomethingproductrelated(expr),
>
> ?.
>
> [sin,cos,tan] ->
> dosomethingtrigrelated(expr),
>
> Otherwise -> error("what should I
> do with", expr, "?")));
>
>
>
> I hope you agree with me that this is an improvement over if then else if
> then else?.
>
>
>
> The attached file implements both case and cond now.
>
> The use of "->" as a separator is actually not imposed by the file, and
> you can use any non-commuting binary or nary operators such as [ , , ?] or :
> or :: or make up something else like --|> ?
>
>
>
> RJF
>
>
>
>
> ------------------------------
>
> *From:* maxima-bounces at math.utexas.edu [mailto:
> maxima-bounces at math.utexas.edu] *On Behalf Of *Alasdair McAndrew
> *Sent:* Sunday, January 07, 2007 1:05 PM
> *To:* maxima list
> *Subject:* Re: [Maxima] Extending maxima language
>
>
>
> I'd like the "if" statement amended to include "elseif"; for example:
>
> if a=b then return(a) elseif a<b return(b-a) else return(b);
>
> Currently there's no way of doing this without placing a second "if"
> statement inside a "block" which is clumsy. If there was no restriction on
> the number of elseif's then this would obviate the need for a case
> statement, and also fit nicely into Maxima's current syntax.
>
> -Alasdair
>
> On 1/8/07, *Andrej Vodopivec* <andrej.vodopivec at gmail.com> wrote:
>
> Since people are discussing a new case statement for maxima I propose
> we add some more stuff at the same time.
>
> Currently I can think of three things which I would like to have in
> maxima. I think I would like to have 2) and 3) even more that 1).
>
> 1) cond statement (with whatever syntax)
>
> 2) assignments to lists:
> something like [a,b,c] == [1,2,3] would be equivalent to a:1, b:2,
> c:3. This could be done by extending : to work in this case or adding
> a new operator == or similar.
>
> 3) unwind_protect:
> I think Barton had an implementation which he posted to this list.
>
> Andrej
> _______________________________________________
> Maxima mailing list
> Maxima at math.utexas.edu
> http://www.math.utexas.edu/mailman/listinfo/maxima
>
>
>
>