For review: PEP 308 - If-then-else expression

[Erik Max Francis]

Piet van Oostrum wrote:

> It just dawned on me that the 'if' is not really necessary.
> "->" would be a more pythonic operator than "?" I think, because it
> stands
> out more. And indeed it looks a bit strange to have the other part as
> a
> keyword.

I agree that if you're not going to have the original ?: form, then
using ? and a keyword is not going to be pretty.

> What about:
>         condition -> (true part, false part)
> The (,) is not a tuple here but it belongs to the -> and the -> says
> to
> select one of the expressions based on the condition and evaluate
> that;
> kind of lazy indexing.

I don't know, it's not really blowing my skirt up.  It lacks a certain
transparency to it; I mean, if I'm new to the language and I see

	safeSqrtX = if x > 0.0 then math.sqrt(x) else 0.0

[setting aside for the time being the issue of the adding of the keyword
`then'] then I have a pretty good chance of understand what that's
supposed to mean.

I must say that I don't find p -> (x, y) too offensive, so that's an
awfully good start.

> We could then also have one for ints rather than bools:
> 
>         i -> [ v_0, v_1, v_2, ... ]
> which would pick v_i and evaluate that.
> Also here the [ ] is not really a list notation but belongs to the ->.

I don't know if this makes sense; if i counts from 0, then 

	condition -> (x, y)

would be 

	bool(condition) -> [y, x]

right?  That would seem to lead to confusion to me.

For the record, I have no problem with introducing a form that extends
to multiway choices, and just has the conditional operator as a
degenerate case.

-- 
 Erik Max Francis / max at alcyone.com / http://www.alcyone.com/max/
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