Reuse 'do' keyword instead of hash sign (#)

[Dan Smith]

Generally speaking, you're right -- keywords are for statements.  But there is one exception: 'new'; arguably, lambda expressions and class instance creations fall into a similar class of expressions.

(As a slight digression, I think the 'if' vs. '?' parallel is useful to consider:

if (cond) statement1; else statement2;
cond ? expr1 : expr2

Some points:
- The statement form uses keywords; the expression form uses obscure operator characters.
- Programmers seem to be comfortable understanding which to use in which contexts.
- The expression form is _not_ enclosed in delimiters, and requires some "lookahead" to mentally process.

Further generalizations depend on how you feel about '?:'.  Perhaps it's a good example to model lambda expressions after.  Or perhaps it's a poorly-designed feature that scares too many beginners away, and we shouldn't use it as a model.)

—Dan

On Jun 20, 2011, at 12:11 AM, Stephen Colebourne wrote:

> No from me too.
> (Keywords introduce statements in Java, not expressions.)
> Stephen
> 
> 2011/6/18 Marcin Wiśnicki <mwisnicki at gmail.com>:
>> This is a repost from 2010/8 since apparently now syntax is up for
>> discussion but wasn't back then.
>> Also I didn't like any proposal from "Syntax poll" thread ;(
>> 
>> You can call it "do" syntax ;)
>> I didn't have the time to think it thoroughly or follow recent java7/8
>> developments but here it goes:
>> 
>> Would it be possible to change the clumsy '#' operator to 'do' keyword ?
>> I.e.:
>> 
>>  do()(5)
>>  do(){return 5;}
>>  do(int x, int y) { if (x>y) return x; else return y; }
>>  button.onClick(do(Event e) { println("button clicked"); });
>> 
>> "strawman" syntax example:
>> 
>>  list.filter( #(Foo t)(t.length() > 3) )
>>      .map( #(Foo t)(t.barCount) )
>>      .max();
>> 
>> becomes:
>> 
>>  list.filter( do(Foo t)(t.length() > 3) )
>>      .map( do(Foo t)(t.barCount) )
>>      .max();
>> 
>> I find it more readable; using special characters feels a bit
>> like perl (noisy), especially when combining multiple lambdas.
>> It even makes sense if you parse it as english.
>> 
>> Don't know what to do with anonymous function type but it could remain as '#'.
>> 
>> Pros:
>>  - more readable
>>  - makes sense
>>  - like '#' needs only 1-lookahead to disambiguate from do-while '(' vs '{' [1]
>>  - did I mention it's more readable ?
>> 
>> Cons:
>>  - none (that I could think of)
>> 
>> [1] Automatic Resource Management from Coins wanted to use 'do' but I
>> see they have switched to 'try' so no problem there.
>> 
>> PS. Please CC me when responding, thanks.
>> 
>> 
>