(Almost) everything is expression

Allen Wirfs-Brock allen at wirfs-brock.com
Fri Nov 11 09:50:38 PST 2011


On Nov 11, 2011, at 9:13 AM, David Herman wrote:

> On Nov 11, 2011, at 8:19 AM, Mark S. Miller wrote:
> 
>> On Fri, Nov 11, 2011 at 7:40 AM, gaz Heyes <gazheyes at gmail.com> wrote:
>> On 11 November 2011 15:33, Mark S. Miller <erights at google.com> wrote:
>> let a = ({
>> 
>>  print('doing stuff');
>>  100;
>> });
>> 
>> How do you know the difference between a blank block statement and a object literal? Surely it becomes an expression once an assignment occurs anyway. 
>> 
>> Doh! Sorry, I completely mis-thought that. Nevermind.
> 
> Your idea of mandatory parens is still valid (if, IMO, a bit unsatisfyingly verbose) for most statement forms. It's only the block-statement-expression that doesn't work. Hence my do-expressions:
> 
>     http://wiki.ecmascript.org/doku.php?id=strawman:do_expressions
> 
> or Brendan's subtly-disambiguated-block-statement-expressions:
> 
>     http://wiki.ecmascript.org/doku.php?id=strawman:block_vs_object_literal
> 
> If Brendan's idea can be made to work, and it's not too confusing, I'm pretty sure I'd prefer it over do-expressions.

I think you''d be making a mistake to go in that direction.  do-expression is a very good solution that fits very well into the language and does not introduce any new readability ambiguities (coining a phrase, a readability ambiguity is a construct that is not formally ambiguous according to the grammar but which will require mental effort by a human reader to appropriate classify).


> You could simply write:
> 
>     let a = {
>         print('doing stuff');
>         100
>     };
> 
> How gorgeous is that?

not very... when I see a = { I immediate have to start thinking, is this think that follows the =?  Is it block expression?  is it an object literal? is it a block lambda?

but if I see any of:
  let a = do {...
  let a = {|| ...
  let a  = { ... 
I immediately know what follows. That is gorgeous...

> 
> But I suspect as we work on evolving the syntax of object literals, it'll get harder to keep them disambiguated. For example, is this:

we're already there ...



> 
>     let a = {
>         foo(x)
>         {
>             alert(x)
>         }
>     }
> 
> ...equivalent to this?
> 
>     let a = {
>         foo: function(x)
>         {
>             alert(x);
>         }
>     };
> 
> ...or this?
> 
>     let a = {
>         foo(x);
>         {
>             alert(x);
>         }
>     };
> 
> So I just don't know if it's feasible.

And being technically feasible does not make it desirable.  Just remember the phrase: "readability ambiguity"

Allen


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