Re: What happened to the is_ family of functions proposal?

Craig Ringer wrote:
> On 25/09/2010 11:51 AM, Darren Duncan wrote:
>> There should just be a single syntax that works for all types, in the
>> general case, for testing whether a value is a member of that type, or
>> alternately whether a value can be cast to a particular type.
<snip>
>> Pg already gets it right in this regard by having a single general
>> syntax for type casting, the "<value>::<type-name>" and value membership
>> of a type should be likewise.
> 
> or the standard:
> 
> CAST(value AS typename)

Indeed.  The exact syntax doesn't matter to me but the point is that the type 
name is its own lexical element, conceptually a function argument, rather than 
being a substring of another one.

>> Maybe to test if a value can be cast as a type, you can continue the ::
>> mnemonic, say adding a "?" for yes and a "!" for no.
>>
>> For example, "<value>?::<type-name>" tests if the value can be cast as
>> the type and "<value>!::<type-name>" or "not <value>?::<type-name>"
>> tests the opposite. An expression like this results in a boolean.
> 
> Personal opinion here: Blech, if I wanted to use Perl6 I'd do so ;-)

I see that someone has been paying attention.

Yes, the idea of using ? or ! to derive a boolean expression from some other 
expression did indeed come from Perl 6.  The ? means "is so", ! means "is not".  A very useful mnemonic in general.

> Good shorthand, I guess, but a CAST syntax extension or alternate CAST 
> version would be a bonus for readability.

Well, sure.  But something consistent with cast syntax that Pg provides.

-- Darren Duncan