Re: Unary operator after binary operator: legal or not? => Compiler Error

[Robert A Duff <bobduff@shell01.TheWorld.com>]

anon@anon.org (anon) writes:

> In <h%Bri.384485$p47.369566@bgtnsc04-news.ops.worldnet.att.net>, anon@anon.org (anon) writes:
>>This maybe a compiler error.  It seams that my GNAT 2.1 from (NYC) as 
>>well as my GNAT 4.3 (GNU) and my Adacore GNAT 2005 (GPL) all state 
>>the same that it there is a "missing operand". But if you use the 
>>following:
>>       return "+"(Left) & "+"(Right);
>>or 
>>       return (+Left) & (+Right);
>>they both work
>>
>>From LRM 4.4 .. 4.5 and LRM 6.6 states that the unary functions can be 
>>redefined.  The reason I say this may be an compiler error is because 
>>the following will still give the same error: 
>>
>>Compiling: xyz.adb (source file time stamp: 2007-07-30 03:00:04)
>>
>>     1. 
>>     2. function Xyz (Left, Right : in integer) return integer is
>>     3. 
>>     4. begin -- Xyz
>>     5.     if +Left <= +Right then
>>     6.        return +Left * +Right;
>>                             |
>>        >>> missing operand
>>
>>     7.     end if;
>>     8. end Xyz;
>>
>
> Forgot to add, in my modified math version, if you replace the "+Right" 
> with "+7" which is a simple_expression it still will give an error. And 
> because you could replace the "+7" with "-7", for negative numbers, 
> which is also a simple_expression you still get an error. This means you 
> have found a compiler error!
>
> This needs to be reported!

If there's a bug, it's a bug in the language definition.  ;-)

GNAT is correctly implementing the syntax rules, here.
"X * +7" and "X * -7" and "X * -Y" and so forth are
all illegal.  See RM-4.4.

There is a similar example in RM-4.5(17), with the comment
"-- parentheses are necessary".

This has nothing to do with user-defined operators.
It's just the syntax rules -- defining your own
operators doesn't change the syntax.

- Bob