[Python-ideas] Statements vs Expressions... why?

[Leonardo Santagada]

On Sep 10, 2008, at 6:22 PM, Cliff Wells wrote:

> On Wed, 2008-09-10 at 21:46 +0200, Christian Heimes wrote:
>> Cliff Wells wrote:
>>> Any thoughts on this?  I'm sure it's been brought up before, but I
>>> haven't found any definitive discussions on why this rather  
>>> arbitrary
>>> design decision continues to hold in the face of a general migration
>>> away from imperative languages (especially when it seems it could be
>>> changed without much backwards-compatibility issues).
>>
>> Two thoughts:
>>
>> Please elaborate how you like to change the syntax of Python.
>
> No changes.  Simply lifting of a particular restriction.

Two restrictions, both that statements can be used in place of  
expressions and that statements now return values. But please explain  
how to do it in a way that is clear. It's a plus if it is backwards  
compatible :)

>> I like to
>> see some concrete examples how your syntax would look like. I also  
>> like
>> to know how your are planing to implement features like lazy  
>> evaluation.
>> The if else ternary operator statement is evaluated lazy. The same
>> construct as expression wouldn't be lazy any more.
>
> Why not?
>
> a = (
>    if a > 1 then:
>        long_calculation()
>    else:
>        other_long_calculation()
> )
>
> Clearly only one of these blocks would be evaluated at runtime.

And now ifs return a value

>>
>> Secondly any syntax change won't happen until we start planing Python
>> 4000 ;)
>
> Yes, that's my expectation, although hopefully PyPy will make some of
> these things possible to experiment with well before then =)

You can do that now in PyPy or any other python version... or maybe  
use Logix to show us a proof of concept version: http://www.livelogix.net/logix/

Now if I remeber correctly this is already the case of logix, look at:
http://www.livelogix.net/logix/tutorial/3-Introduction-For-Python-Folks.html#3.1

Why would you need lambda then? couldn't you just write x = def (x,y):  
return x+y ?