December 11, 2007
>   sort!("a > b")(array);

I just wanted to say that this is BRILLIANT!  Zero call overhead, zero syntax overhead, compile-time lambda functions!

All the algorithms should support this syntax so we can do sexy compile-time lambda one-liners like:

   find!("a.some_member > 10")(array);

or

   partition!("a.call_something() !is null")(array);

etc.

And probably those should allow a data arg passed as 'b' to the lambda function so you could do something like
   find!("a.some_member > b")(array, 10);

Or even use template varargs and number the args automatically to allow:

   find!("a.x > b && a.w < c")(array, 10, 20);

It would just sequentially name the arguments b,c,d,e... etc.

Or even make it like C#/Tango's format string patterns since the string can be processed before mixing it in.
   find!("a.x > {1} && a.w < {2}")(array, 10, 20);

That would be excellent.  Take that boost::lambda!

--bb
December 11, 2007
"Bill Baxter" <dnewsgroup@billbaxter.com> wrote in message news:fjl4fo$8am$1@digitalmars.com...
> >   sort!("a > b")(array);
>
> I just wanted to say that this is BRILLIANT!  Zero call overhead, zero syntax overhead, compile-time lambda functions!
>
> All the algorithms should support this syntax so we can do sexy compile-time lambda one-liners like:
>
>    find!("a.some_member > 10")(array);
>
> or
>
>    partition!("a.call_something() !is null")(array);
>
> etc.
>
> And probably those should allow a data arg passed as 'b' to the lambda
> function so you could do something like
>    find!("a.some_member > b")(array, 10);
>
> Or even use template varargs and number the args automatically to allow:
>
>    find!("a.x > b && a.w < c")(array, 10, 20);
>
> It would just sequentially name the arguments b,c,d,e... etc.
>
> Or even make it like C#/Tango's format string patterns since the string
> can be processed before mixing it in.
>    find!("a.x > {1} && a.w < {2}")(array, 10, 20);
>
> That would be excellent.  Take that boost::lambda!
>
> --bb

Yes very cool!  Would be even better if the parens could be removed. Ideally, the compiler would be able to do CTFE with some lambdas.

-Craig


December 11, 2007
Craig Black wrote:
> "Bill Baxter" <dnewsgroup@billbaxter.com> wrote in message news:fjl4fo$8am$1@digitalmars.com...
>>>   sort!("a > b")(array);
>> I just wanted to say that this is BRILLIANT!  Zero call overhead, zero syntax overhead, compile-time lambda functions!
>>
>> All the algorithms should support this syntax so we can do sexy compile-time lambda one-liners like:
>>
>>    find!("a.some_member > 10")(array);
>>
>> or
>>
>>    partition!("a.call_something() !is null")(array);
>>
>> etc.
>>
>> And probably those should allow a data arg passed as 'b' to the lambda function so you could do something like
>>    find!("a.some_member > b")(array, 10);
>>
>> Or even use template varargs and number the args automatically to allow:
>>
>>    find!("a.x > b && a.w < c")(array, 10, 20);
>>
>> It would just sequentially name the arguments b,c,d,e... etc.
>>
>> Or even make it like C#/Tango's format string patterns since the string can be processed before mixing it in.
>>    find!("a.x > {1} && a.w < {2}")(array, 10, 20);
>>
>> That would be excellent.  Take that boost::lambda!
>>
>> --bb
> 
> Yes very cool!  Would be even better if the parens could be removed. Ideally, the compiler would be able to do CTFE with some lambdas.

There's that idea of creating "static" parameters from DCon07.

With that you should be able to stick the string in as a regular parameter.  But I don't actually find the template syntax too bad.  It's a good reminder that the argument must be a compile-time constant.

When/if we get static parameters it's going to be harder to tell from looking at code what's compile-time and what's not.  I anticipate wasting lots of time in this manner: "why did I/they write this function like this?  thats silly <rewrite rewrite> -- oh damn, I see why now. Argument #3 has to be a compile-time constant."

--bb
December 12, 2007
"Bill Baxter" <dnewsgroup@billbaxter.com> wrote in message news:fjmol3$1f71$1@digitalmars.com...
> Craig Black wrote:
>> "Bill Baxter" <dnewsgroup@billbaxter.com> wrote in message news:fjl4fo$8am$1@digitalmars.com...
>>>>   sort!("a > b")(array);
>>> I just wanted to say that this is BRILLIANT!  Zero call overhead, zero syntax overhead, compile-time lambda functions!
>>>
>>> All the algorithms should support this syntax so we can do sexy compile-time lambda one-liners like:
>>>
>>>    find!("a.some_member > 10")(array);
>>>
>>> or
>>>
>>>    partition!("a.call_something() !is null")(array);
>>>
>>> etc.
>>>
>>> And probably those should allow a data arg passed as 'b' to the lambda
>>> function so you could do something like
>>>    find!("a.some_member > b")(array, 10);
>>>
>>> Or even use template varargs and number the args automatically to allow:
>>>
>>>    find!("a.x > b && a.w < c")(array, 10, 20);
>>>
>>> It would just sequentially name the arguments b,c,d,e... etc.
>>>
>>> Or even make it like C#/Tango's format string patterns since the string
>>> can be processed before mixing it in.
>>>    find!("a.x > {1} && a.w < {2}")(array, 10, 20);
>>>
>>> That would be excellent.  Take that boost::lambda!
>>>
>>> --bb
>>
>> Yes very cool!  Would be even better if the parens could be removed. Ideally, the compiler would be able to do CTFE with some lambdas.
>
> There's that idea of creating "static" parameters from DCon07.
>
> With that you should be able to stick the string in as a regular parameter.  But I don't actually find the template syntax too bad.  It's a good reminder that the argument must be a compile-time constant.
>
> When/if we get static parameters it's going to be harder to tell from looking at code what's compile-time and what's not.  I anticipate wasting lots of time in this manner: "why did I/they write this function like this?  thats silly <rewrite rewrite> -- oh damn, I see why now. Argument #3 has to be a compile-time constant."
>
> --bb

First I've heard about static parameters  Very good idea.

You may be right about all that, but I still prefer a syntax without double quotes.


December 12, 2007
Bill Baxter wrote:
> When/if we get static parameters it's going to be harder to tell from looking at code what's compile-time and what's not.  I anticipate wasting lots of time in this manner: "why did I/they write this function like this?  thats silly <rewrite rewrite> -- oh damn, I see why now. Argument #3 has to be a compile-time constant."

The way I figure they should be used only when overloading between "known at compile time" and "not known at compile time". For instance, precompiling stuff like formatting strings and regexps. If a parameter is only for compile time use in that it doesn't compile with a non-const argument, it should be a template parameter as currently.

But then, I think using CTFE for something that is used only at compile time is completely wrong, so I might be alone with my opinions. :-)

-- 
E-mail address: matti.niemenmaa+news, domain is iki (DOT) fi
December 12, 2007
On 12/12/07, Craig Black <cblack@ara.com> wrote:
> >   sort!("a > b")(array);
>
> I still prefer a syntax without double quotes.

How about

    sort!(q{a > b})(array);

? D2 rocks!
December 12, 2007
Janice Caron:
> sort!(q{a > b})(array);

Please explain :-)

Bye,
bearophile
December 12, 2007
"bearophile" <bearophileHUGS@lycos.com> wrote in message news:fjpcqv$1uio$1@digitalmars.com...
> Janice Caron:
>> sort!(q{a > b})(array);
>
> Please explain :-)
>
> Bye,
> bearophile

q{ ... } is a "token string".  Its contents are lexed and have to conform to D's lexicography, but it is then turned into a string literal.  It goes well with string mixins and the like.


December 12, 2007
On 12/12/07, bearophile <bearophileHUGS@lycos.com> wrote:
> Janice Caron:
> > sort!(q{a > b})(array);
>
> Please explain :-)

It's just another way of writing strings. You can write "..." or you can write q{...}. It's slightly different - escape strings aren't expanded, and the string contents have to be valid D, but it's still just a string. The cool thing is that your text editor doesn't know that, and so will still syntax-highlight the string contents!
December 18, 2007
Bill Baxter wrote:
>  >   sort!("a > b")(array);
> 
> I just wanted to say that this is BRILLIANT!  Zero call overhead, zero syntax overhead, compile-time lambda functions!
> 
> All the algorithms should support this syntax so we can do sexy compile-time lambda one-liners like:
> 
>    find!("a.some_member > 10")(array);
> 
> or
> 
>    partition!("a.call_something() !is null")(array);
> 
> etc.

This is a pretty neat trick that has the benefit of providing a succinct syntax that works for both runtime and for CTFE.  However, the overall utility of the approach seems less than is offered by more traditional means.  Complex comparisons could render the function call largely unreadable by requiring a multi-line string to be passed as a template argument, and there is also no means of supplying a comparator at run-time using this method.  For comparison, consider this find routine:

    template find( Elem, Pred = IsEqual!(Elem) )
    {
        size_t find( Elem[] buf, Elem pat, Pred pred = Pred.init )
        {
            for( size_t pos = 0; pos < buf.length; ++pos )
            {
                if( pred( buf[pos], pat ) )
                    return pos;
            }
            return buf.length;
        }
    }

With this support comparator:

    struct IsEqual( T )
    {
        static bool opCall( T p1, T p2 )
        {
            static if( is( T == class ) || is( T == struct ) )
                return (p1 == p2) != 0; // opEquals returns an int
            else
                return p1 == p2;
        }
    }

Because the function used for comparison is static, this code complies and works perfectly with CTFE.  At the same time, the predicate may also be a more complex struct, anonymous delegate, function pointer, named delegate, and so on.  With this in mind, I would be inclined to do something like this to add string predicate support to existing routines:

    template find( char[] oper )
    {
        size_t find(Elem)( Elem[] buf, Elem pat )
        {
            return .find!(Elem, Encode!(Elem, oper))( buf, pat );
        }
    }

    struct Encode( T, char[] exp )
    {
        static bool opCall( T a, T b )
        {
            return mixin(exp);
        }
    }

Thus allowing:

    const posA = find( "abcdefg", 'c' );            // uses IsEqual
    const posB = find!("a == b")( "abcdefg", 'c' ); // uses Encode

    void main()
    {
        // uses anonymous delegate at run-time
        auto posC = find( "abcdefg",
                          'c',
                          (char a, char b){ return a == b; } );
    }

So I guess what I'm saying is that the string version is a cool idea to be used in addition to the classic approach, but I see little utility in having it replace the classic approach.  And it's easy enough to add the string encoding as a facade over existing functions that nearly anything that accepts a predicate can use the string approach for free.


Sean
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