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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