On 6 January 2014 17:59, Allen Wirfs-Brock <[email protected]> wrote:
> The major new complication of do-expressions is that they allow for the
> occurrence of break/continue/return abrupt completions in contexts such as
> for loop heads where they could not perviously occur. However,
> do-expressions where still on the table when I did the spec. work for
> "completion reform" so the ES6 draft already deals with these abrupt
> completions in those contexts. Even though there is currently no way to
> produce them.
I agree that's a complication, which is why I would propose to
disallow them, at least for the time being. Motivation:
- YAGNI -- I have a hard time coming up with a use case that isn't
obfuscated code (even considering generated code).
- They complicate the semantics and implementation -- for example, you
would have to roll back non-empty expression stacks (in a stack
machine implementation).
- They destroy nice equivalences -- in particular, I'd like "do {...}"
to be equivalent to "(() => {...})()", e.g. to minimise refactoring
hazards.
- We can always allow them later, if the need should ever arise.
Dave, I remember you were in favour of allowing these. Do you have
specific use cases in mind?
/Andreas
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