+1 for option 3. On Sat, Apr 25, 2015 at 1:18 PM, Yury Selivanov <yselivanov...@gmail.com> wrote:
> 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 > > -- --Guido van Rossum (python.org/~guido)
_______________________________________________ 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
