PROPOSAL: open and close brace optional for single statement try, catch, finally, method declaration

Tom Hawtin Thomas.Hawtin at Sun.COM
Mon Mar 30 06:25:01 PDT 2009

Glenn A. Marshall wrote:
> 1.  This example is syntactically invalid since the first try does not have
> a catch nor finally clause; it is not ambiguous.  Good example tho.

Neal's example:

 >> try
 >> try stmt;
 >> catch(...) stmt;
 >> catch(...) stmt;
 >> finally stmt;

Under the proposal "try stmt; catch(...) stmt;" is a statement. So the 
above is equivalent to:

catch(...) stmt;
finally stmt;

But "try stmt; catch(...) stmt; catch(...) stmt;" is also a statement. 
So the example is also equivalent to:

finally stmt;

Which is different. Which is it?

This is similar to the dangling-else ambiguity.

> 2.  The optional omission of the braces is only applicable to simple, single
> statement try, catch, finally (and method declaration).  Braces are still
> allowed, and are required for disambiguation, as well as for multiple
> statement try, catch finally (and method declaration).  They are are needed
> in this example.

That reads as if you think of a block statement (in for example the 
typical while usage) as not a type of statement. A block is a statement. 
You could ammend the grammar so the proposal uses non-block statement, 
but this is not how the rest of the language works.

BTW: Does anyone have a good suggestion for tool and basic Java grammar 
to check that syntax modifications are still parseable?


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