Actually, the "defer:"-syntax is really readable and searchable compared
to the cryptic comparison operator used in the proposal. Just thinking
towards "googleability".
Furthermore, the concept is even more general than parameter definition
of functions and methods. I guess a lot of people have already tryied to
implement this kind of object various times before (proxy objects,
transparent futures etc.)
It also would fit the current semantics of default parameters of Python.
Cheers
Sven
On 24.10.21 16:37, David Mertz, Ph.D. wrote:
On Sun, Oct 24, 2021, 10:11 AM Chris Angelico
Not sure I understand. Your example was something like:
def fn2(thing):
a, b = 13, 21
x = 5
print("Thing is:", thing)
def f(x=defer: a + b):
a, b = 3, 5
fn2(defer: x)
return x
So inside f(), "defer: a + b" will look in f's scope and use the
variables a and b from there, but passing a "defer: x" to fn2 will
use x from f's scope, and then a and b from fn2's?
Yes, basically as you describe. A "deferred object" is basically just
a string that knows to wrap itself in eval() when accessed (maybe
Steven's "thunk" is a better term... But definitely something
first-class, unlike in Algol).
So within fn2() the parameter 'thing' is bound to an object like
'<defer eval("a+b")>'.
Indeed this means that the 'defer:' or 'thunk' or special symbol
spelling, has to decide whether the thing being deferred is already
itself a deferred object. If so, just pass along the identical object
rather than treat it as a new expression.
At least that's what would feel most intuitive to me. But I'm
deliberately not pushing a specific syntax. For example, if we didn't
want to "reuse" the spelling 'defer:' for both creating and passing a
deferred object, we could have different spellings.
def f(x=defer: a + b):
a, b = 3, 5
fn2(noeval: x)
return x
... I don't like that spelling, but just showing the concept.
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