Alternative syntax for closures

[Rémi Forax]

Neal Gafter a écrit :
> On Tue, Jul 15, 2008 at 3:08 PM, Rémi Forax <forax at univ-mlv.fr 
> <mailto:forax at univ-mlv.fr>> wrote:
>
>     Neal Gafter a écrit :
>
>         And how is your method invoked?  
>
>     like that:
>     bolean cond=...
>     myIf(cond) {
>      //true part
>     } {
>      //false part
>
>     }
>
>
> Your syntax is ambiguous.  There is no way to tell if it is to be 
> parsed as a single invocation
>
>    IDENTIFIER ( ARGS ) BLOCK BLOCK
>
> or an invocation followed by a block
>
>    IDENTIFIER ( ARGS ) BLOCK
>    BLOCK
yes, the syntax is ambiguous but it can be solved by prefering the former
than the later.
>
>
>         How do I get exception transparency for non-trailing arguments?
>
>     There is no way.
>
>
> Then I presume there is also no way to declare local variables or 
> fields to store closures that have parametric exceptions, which rules 
> out a number of useful control APIs.  Your proposal is not just a 
> different syntax for the same semantics; it supports only a subset of 
> the useful functionality of BGGA.
Not exactly.
Closure block types are used internally by the compiler but can't be 
declared by a user.
If you want to store such closure in a local variable or a field, you 
have to convert it
to a function type.

The idea behind is that if you store a closure block in a field (or a 
final/shared local field)
you have lot of chance to get an exception at runtime.

By example, this code (BGGA syntax) may work or not
depending if you have return/break/continue
in the closure block.

Executor executor=...
...
<throws E> void fork(
     final {=>void throws E} block) throws E {
  executor.submit(new Runnable() {
    public void run() {
       block.invoke(); // need a try/catch E here
    }
  });
}

The same example with my syntax

void fork() block() {
  final void() throws Exception b =
   (void() throws Exception)block; // cast is needed here
  executor.submit(new Runnable() {
    public void run() {
       b.invoke(); // try/catch Exception needed here
    }
  });
}

I don't see a difference with BGGA's functionality.

Rémi