Re: Add syntax highlighting to own command
- To: mathgroup at smc.vnet.net
- Subject: [mg101899] Re: Add syntax highlighting to own command
- From: earthnut at web.de (Bastian Erdnuess)
- Date: Tue, 21 Jul 2009 03:52:53 -0400 (EDT)
- References: <200907090600.CAA17547@smc.vnet.net> <h3766u$f9h$1@smc.vnet.net> <h41f80$rkq$1@smc.vnet.net>
Leonid Shifrin <lshifr at gmail.com> wrote:
> Hi Bastian,
>
> If I understand you correctly and the last rule you added
>
> ( Let /: ( lhs_ := Let[ vars_, expr_ /; cond_ ] ) :=
> Let[ vars, lhs := expr /; cond ])
>
> is to allow shared local variables in function definitions (like with
> standard With, Module or Block), then your code does not work for me.
Yes, you are (and understood me) right.
> Consider the following definition:
> [...]
> f[x_, y_] :=
> Let[{xl = x, yl = y + xl + 1}, xl^2 + yl^2 /; (xl + yl < 15)];
I tried first something different than I actually posted. I thought
then I could write it different. But somehow I must have forgotten to
test it correctly.
However, also with my original version (something like
f_[ l_, Let[ r_ ] ] := bla[ l := r ] /; f == SetDelayed )
I would have gotten about
f[ x$_, y$_ ] := x^2 + (1 + x + y)^2 /; 1 + 2x + y < 15 .
I didn't recognized that the local variables in f get renamed.
> I can think of several reasons why this does not work, and will expand this
> discussion if you will be interested, but here is the version that I
> believe does work:
Now, I can too. But if you want to explain some of your reasons, i'll
hear.
I also found a trick to get around the renaming problem (using your
Verbatim instead of mine f_[...] /; f == ...):
Verbatim[ SetDelayed ][ l_,
Let[ v_, Verbatim[ Condition ][ r_, c_ ] ]
] ^:=
Let[ v,
SetDelayed[ #, r /; c ] & @ ToExpression @ #
] & @ ToString[ l, InputForm ]
This passes basically the left hand side as string around the issue with
the renaming.
The last days I often figured out that that what I think of as "syntax
transformation" or Simon called "passing unevaluated arguments around"
works best by passing the things around as strings. Are there
disadvantages doing that? I could imagine that this might be not the
best if one wants to compile the source -- but so far I'm far away from
starting to try to understand Mathematicas compiler.
> [ Block trick ]
> This uses the Block trick. It is actually a true macro, since
> it expands the code before SetDelayed acts on it:
That seems to be a nice trick. Thank you for showing that. I need to
think a little bit about that to decide if I like it for this situation.
Regards,
Bastian
- References:
- Add syntax highlighting to own command
- From: earthnut@web.de (Bastian Erdnuess)
- Add syntax highlighting to own command