BNF Question
Kirk McDonald
kirklin.mcdonald at gmail.com
Sun Sep 2 22:53:30 PDT 2007
BCS wrote:
> Reply to Xinok,
>
>> An equal expression is when the data in two objects is compared.
>> int[] arr1 = [10, 20, 30], arr2 = [10, 20, 30];
>> if(arr1 == arr2){ } // True
>> An identity expresion is when the pointer values (and .length in
>> arrays)
>> in two objects is compared.
>> int[] arr1 = [10, 20, 30], arr2 = arr1;
>> if(arr1 is arr2){ } // True
>> For primitive types, there is no difference between using == and is.
>> int a = 15, b = 15;
>> if(a == b){ } // True
>> if(a is b){ } // True
>> BCS wrote:
>>
>
> However what you describe is at the semantic level and the grammar is
> totally at the syntax level. What I was looking at is that this:
>
> a is b
>
> can be parsed as an Identity Expression and an Equal Expression.
>
> If the distinction is a semantic issue then this makes D context
> sensitive. If it is not a semantic issue, then it is redundant or
> conflicting.
>
The grammar is merely confusing. It might be better written as:
EqualExpression:
ShiftExpression
ShiftExpression == ShiftExpression
ShiftExpression != ShiftExpression
IdentityExpression
--
Kirk McDonald
http://kirkmcdonald.blogspot.com
Pyd: Connecting D and Python
http://pyd.dsource.org
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