Re: [PyX-devel] Re: [PyX-checkins] pyx/test/experimental solve.py,1.2,1.3

[Andre W. <wo...@us...>]

Hi,

On 28.07.04, Magnus Lie Hetland wrote:
> Joerg Lehmann <jo...@us...>:
> >
> [snip]
> > IMHO it's too implicit. In particular, not having to explicitly specify
> > the solver is probably not a good idea. 
> 
> I think using == for anything with side-effects (or even anything that
> isn't interpretable as a boolean equality check) is quite unfortunate.
> It might *look* good, but still... (if x == y: alwaysexecuted()...)

Thanks, Jörg, Magnus. I was not satisfied myself. The comparison makes
me troubles as well ... see the id comparision and the XXX comment,
where I check for zero using "is", which works, since all integer
constants below 100 are predefined and used by reference. In the
beginning I liked the idea, but its probably a bad idea.

> If one was feeling adventurous, one could even do stuff like
> 
>   solver(x = y)
> 
> but only for single-variable left-hand-sides, of course.

I do not quite understand. What's the result of an assignment? Anyway,
once we do not use x == y, we should allow for x = y as well. Its
becoming even less symmetric: Currently you need to set x and y to be
scalar instances (or variable instances). In your case this becomes
assymetric. You would need to initialize just x.

Beside that, I think where might be usecases, where you store a term.
Say:

x = scalar()
y = scalar()
z = scalar()

A = x + 5*y
B = A + y
C = A + z

solver.eq(B, C)

I don't know whether this will make sense, but you can do so.

> It would be possible to do some property magic too... I'm pretty sure
> I could write code such that
> 
>   a.x = b.y
>   a.y = b.x
> 
> could be turned into a set of equations (by using wrapper classes
> around the objects returned by the properties, somewhat like bound
> methods).
> 
> Just musing.

You can currently do so with the "==" logic. That's because the
components of a vector ar scalars and you can formulate scalar
eqations and vector equations. So you can currently write:

a = vector(2)
b = vector(2)

a[0] == b[1]
a[1] == b[0]

Note I have not (yet) a getattr on the vectors for "x", "y", "z". But
right, thats trivial to be added.

Now you can write:

a == point(0, 1)

Guess, what b becomes? ... ;-)


André

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