Hi Guido,
On 2015-04-24 1:03 PM, Guido van Rossum wrote:
*3. syntactic priority of `await`*
Yury, could you tweak the syntax for `await` so that we can write the most
common usages without parentheses? In particular I'd like to be able to
write
```
return await foo()
with await foo() as bar: ...
foo(await bar(), await bletch())
```
(I don't care about `await foo() + await bar()` but it would be okay.)
```
I think this is reasonable with some tweaks of the grammar (similar to what
Greg did for cocall, but without requiring call syntax at the end).
I've done some experiments with grammar, and it looks like
we indeed can parse await quite differently from yield. Three
different options:
Option #1. Parse 'await' exactly like we parse 'yield'.
This how we parse 'await' in the latest version of reference
implementation.
Required grammar changes:
https://gist.github.com/1st1/cb0bd257b04adb87e167#file-option-1-patch
Repo to play with:
https://github.com/1st1/cpython/tree/await
Syntax:
await a()
res = (await a()) + (await b())
res = (await (await a()))
if (await a()): pass
return (await a())
print((await a()))
func(arg=(await a()))
await a() * b()
Option #2. Keep 'await_expr' in 'atom' terminal, but don't
require parentheses.
Required grammar changes:
https://gist.github.com/1st1/cb0bd257b04adb87e167#file-option-2-patch
Repo to play with (parser module is broken atm):
https://github.com/1st1/cpython/tree/await_noparens
Syntax:
await a()
res = (await a()) + await b() # w/o parens (a() + await b())
res = await await a()
if await a(): pass
return await a()
print(await a())
func(arg=await a())
await a() * b()
Option #3. Create a new terminal for await expression between
'atom' and 'power'.
Required grammar changes:
https://gist.github.com/1st1/cb0bd257b04adb87e167#file-option-3-patch
Repo to play with (parser module is broken atm):
https://github.com/1st1/cpython/tree/await_noparens2
Syntax:
await a()
res = await a() + await b()
res = await (await a()) # invalid syntax w/o parens
if await a(): pass
return await a()
print(await a())
func(arg=await a())
await (a() * b()) # w/o parens '(await a() * b())
I think that Option #3 is a clear winner.
Thanks,
Yury
_______________________________________________
Python-Dev mailing list
Python-Dev@python.org
https://mail.python.org/mailman/listinfo/python-dev
Unsubscribe:
https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
