On 2015-09-19 17:21, Guido van Rossum wrote:
"Uptalk" is an interesting speech pattern where every sentence sounds like a question. Google it, there's some interesting research.
The "null pattern" is terrible. Uptalk should not be considered a unary operator that returns a magical value. It's a modifier on other operators (somewhat similar to the way "+=" and friends are formed).
In case someone missed it, uptalk should test for None, not for a falsey value.
I forgot to think about the scope of the uptalk operator (i.e. what is skipped when it finds a None). There are some clear cases (the actual implementation should avoid double evaluation of the tested expression, of course):
a.b?.c.d[x, y](p, q) === None if a.b is None else a.b.c.d[x, y](p, q) a.b?[x, y].c.d(p, q) === None if a.b is None else a.b[x, y].c.d(p, q) a.b?(p, q).c.d[x, y] === None if a.b is None else a.b(p, q).c.d[x, y]
But what about its effect on other operators in the same expression? I think this is reasonable:
a?.b + c.d === None if a is None else a.b + c.d
OTOH I don't think it should affect shortcut boolean operators (and, or):
a?.b or x === (None if a is None else a.b) or x
It also shouldn't escape out of comma-separated lists, argument lists, etc.:
(a?.b, x) === ((None if a is None else a.b), x) f(a?.b) === f((None if a is None else a.b))
Should it escape from plain parentheses? Which of these is better?
(a?.b) + c === (None if a is None else a.b) + c # Fails unless c overloads None+c (a?.b) + c === None if a is None else (a.b) + c # Could be surprising if ? is deeply nested
It shouldn't escape beyond anything having a lower precedence.
Here are some more edge cases / hypergeneralizations:
{k1?: v1, k2: v2} === {k2: v2} if k1 is None else {k1: v1, k2: v2} # ?: skips if key is None # But what to do to skip None values?
Could we give ?= a meaning in assignment, e.g. x ?= y could mean:
if y is not None: x = y
Shouldn't that be: if x is not None: x = y ? It's the value before the '?' that's tested.
More fun: x ?+= y could mean:
if x is None: x = y elif y is not None: y += y
Or: if x is None: pass else: x += y
You see where this is going. Downhill fast. :-)
Could it be used postfix: a +? b === None if b is None else a + b -?a === None if a is None else -a or both prefix and postfix: a ?+? b === None if a is None or b is None else a + b ?