block-lambda revival

Rob Campbell rcampbell at mozilla.com
Fri Jun 24 06:15:46 PDT 2011


On 2011-06-23, at 22:37, Brendan Eich wrote:

> On Jun 23, 2011, at 4:07 PM, Rob Campbell wrote:
> 
>> I'm liking the block-lambda syntax, I think more than the arrow. One possible shortening could be to exclude the second bar (|) if no argument variables are specified.
>> 
>> {| // some block of code };
> 
> This does not work. How do you know that what follows the first | is not a formal parameter?

Ah, right. I guess you'd need to scan the full block first and look for the second | and then do the right thing for each case. Messy.

> Formal parameter syntax looks like expression syntax -- currently Expression covers FormalParameterList. Arrow function syntax relies on this.
> 
> /be
> 
>> 
>> I don't *think* we'd ever start an expression with a single | operator, so there should be no ambiguity.
>> 
>> On 2011-06-23, at 19:27, Brendan Eich wrote:
>> 
>>> On Jun 23, 2011, at 3:14 PM, Jorge wrote:
>>> 
>>>>> Anyway, my 2 cents.  Thanks!
>>>> 
>>>> {|| ... } for shorter *function* syntax is my favorite too. +1(e9)
>>> 
>>> Thanks -- I am continuing to maintain arrow function syntax and block lambda revival as strawmen.
>>> 
>>> Arrows now require only two-token lookahead, ignoring the #!~ prefixes proposed for non-configurable, non-writable, and non-enumerable property assignments in object initialisers. This is in order to support either an object literal body or a braced non-empty block body where the block's first statement is not a labeled statement.
>>> 
>>> Block lambda revival has more grammar changes, but so far they check out.
>>> 
>>> 
>>>> Also, if any { block } could be a lambda, perhaps we won't need that (nor any new) syntax for block-lambdas.
>>> 
>>> We would need new syntax still, for formal parameters.
>>> 
>>> Making blocks be expressions requires unifying the ObjectLiteral and Block productions. I don't know how to do this in without at least two-token lookeahead, and it is not a backward compatible change if done for all places where Statement : Block in the current grammar.
>>> 
>>> 
>>>> Also, I'd prefer to know/see clearly when a function is being call()ed, so I'm not very fond of paren-free calls: foo(bar) is clearly an invocation, unlike foo bar,
>>> 
>>> Your example is too abstracted to be fair. Concretely, the latter will *always* look like foo {|| bar} ... and never foo bar for any bar.
>>> 
>>> 
>>>> and readability is more important than saving a few keystrokes.
>>> 
>>> Readability arguments support the paren-free syntax too. You can't win this by selective arguing.
>>> 
>>> 
>>>> The C language is still (and -ISTM- will be for a long time) important, so -IMO- every little bit of JS's C-like syntax is a plus: less to learn: an old, popular, widely used, well-known, and familiar syntax.
>>> 
>>> C by way of Java, and both are boat anchors. Again, where pray tell is 'function' in C?
>>> 
>>> 
>>>> JS -unlike other languages- is important enough that it does not need to follow these (dubious) trendy fashions to become popular. Nor to survive.
>>> 
>>> Nothing trendy about Smalltalk blocks unless you are a Rubyist.
>>> 
>>> 
>>>> Proper punctuation aids comprehension and we're programming, not writing quick SMSs.
>>> 
>>> This is silly, you're making vague arguments that cut both ways.
>>> 
>>> /be
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>> 
> 

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