[Python-Dev] Re: decorators and 2.4

[Jeff Bone]

On Jun 28, 2004, at 12:27 PM, David Abrahams wrote:

> I'm a big fan of declarative programs.

BTW, for the record --- I'm not under any illusions about Python's 
"declarativeness."  ;-)

> That said, declarativeness (especially in Python) is more a matter of
> "notational flavor" than anything we can measure.  It's certainly
> independent of whether there are actual side-effects.
>
> Also, I'm suspicious of any heroic efforts to prevent language
> features from being "abused".

Let me be specific about what I'm actually worried about, here.  
Specifically:  I've been playing a bit with some type-inferencing stuff 
and optional typing.  One desiderata for decorators, per the PEP, is to 
support applications like embedding type signatures and so forth into 
the language, attaching them to the relevant objects.  A goal could be 
to support at least partial compilation with (some, and optional) 
compile-time guarantees about type safety and behavior.  To the extent 
that decorators either (a) are evaluated conditionally based on runtime 
state, or (b) modify and are in turn modified by runtime state, 
decorators as mutable environments or with true side effects make a 
mess of that.  Perhaps you don't really want "decorators" for that --- 
perhaps you want "macros."  Subtle but IMHO important distinction.

NB, I'm no type Nazi.  But I'd really like to see (a) Python 
implemented in Python, someday --- it would make playing with all these 
sorts of languages ideas and moving the language along a LOT easier, 
and (b) Python compiling easily to (and running well on) arbitrary 
machines or virtual machines.  The more runtime / imperative / 
conditional / side-effecting behavior we allow for decorators, the more 
difficult both of those goals become.

Not trying (heroically or otherwise) to keep language features from 
being abused as much as simply ask the question "have we REALLY thought 
through the use cases, the alternatives, and their impact on the future 
of the language."

jb