On Wed, Jun 26, 2013 at 2:19 PM, Robert Dodier <robert.dodier at gmail.com>wrote:
> On 2013-06-23, Barton Willis <willisb at unk.edu> wrote:
>
> > The function sublis controls evaluation of lambda forms using mqapply
> > (not mquote):
>
> Thanks for the reminder -- I had forgotten about that.
>
> > (%i3) sublis(['sin =3D lambda([x],42)], sin(z)), sublis_apply_lambda :
> false;
> > 1> (MSUBLIS-SUBST ((%SIN SIMP) $Z) T)
> > 2> (MSUBLIS-SUBST ($Z) NIL)
> > 3> (MSUBLIS-SUBST $Z T)
> > <3 (MSUBLIS-SUBST $Z)
> > 3> (MSUBLIS-SUBST NIL NIL)
> > <3 (MSUBLIS-SUBST NIL)
> > <2 (MSUBLIS-SUBST ($Z))
> > 2> (MSUBLIS-SUBST %SIN T)
> > <2 (MSUBLIS-SUBST ((LAMBDA SIMP) ((MLIST) $X) 42))
> > <1 (MSUBLIS-SUBST ((MQAPPLY) ((LAMBDA SIMP) ((MLIST) $X) 42) $Z))
> > (%o3) lambda([x],42)(z)
>
> > Maybe $substitute could be modified to use the mqapply trick.
>
> Yeah -- I've been working on that. But I wonder if subst and sublis
> should be merged -- aside from sublis being parallel and subst being
> serial, do they have any different effect? If we are satisfied that
> they are otherwise the same, we could nuke the existing subst and
> have it punt to sublis instead (looping to get serial substitutions).
Agreed: subst/psubst/sublis should be one function internally. sublis
will have to be reworked to use hash tables rather than symbol property
lists because subst is not restricted to symbols, e.g., subst(x,a*b,f(a*b)).
> As for extending the (obscure) option variable sublis_apply_lambda
> > to substitute, I dunno--generally I lean toward fewer (obscure)
> > option variables.
>
> Agreed -- I'm inclined to nuke sublis_apply_lambda.
>
We will need some mechanism to force the transformation
lambda([x],f(x))(y) => f(y). ev(...,lambda) is the obvious convenience
syntax, but I would like to have the functionality be available outside ev,
e.g. lambda_subst(expr).
> Is mqapply used this way a crazy hack that just happens to wrork?
>
? What crazy way? The whole point of mqapply is to allow non-symbols to be
applied to arguments. The crazy part is that Maxima lets you get away with
a lambda-expression in the caar sometimes.
-s
Looks to me like it is working just as one would expect.
>
> best
>
> Robert Dodier
>
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