On 22/08/2008, at 5:27 PM, William Stein wrote:
>
> On Thu, Aug 21, 2008 at 11:28 PM, David Philp
> <[EMAIL PROTECTED]> wrote:
>
>> I hope one can't own such things but I don't want a legal fight.
>
> If I were afraid, then Sage would be nowhere today.
I just don't think Mathematica reimplementation is a worthy enough
thing that it's worth risking a legal fight with Wolfram. There are
other ways to make Sage really good.
>> Otherwise, I agree. A mathematica-like parser would be useful.
>> Though I'd be surprised if the concepts map across well enough for it
>> to be anything other than an ugly hack.
>
> Why?
I don't think it's useful for me to keep going much more until I know
more about sage. But I will explain where the bad feeling came from:
All the explanations that "sage can do that" have involved python
lists, because I used names and examples like 'data = {1, 2, 3}'. But
the power of ReplaceAll (the /. operator) is that it places no
requirements on the form of the 'data' argument.
I.e. the example:
[(0 if d < 0 else d) for d in data]
is an illustration of how to write a for-each expression in python,
but it has nothing much to do with ReplaceAll. The difference is that
ReplaceAll is used for transforming 'data' not 'the elements of data'.
E.g.
x + a*y + z[w + v] /. Plus -> List
yields {x, a y, z[{v, w}]} (That sort of manipulation has been useful
to me sometimes.)
It reads much the same as before: expr, but with sums replaced by lists.
If someone proposes an implementation I can try and shoot it down or
improve it. But I don't know sage well enough to know whether there
is an obvious way to do it all. My guess is that this is a natural
task for Lisp and the wrong task for Python.
D
==================================
David J Philp
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