On 2010-12-19 16:14, Andrei Alexandrescu wrote:
On 12/19/10 5:01 AM, Simen kjaeraas wrote:Walter Bright <newshou...@digitalmars.com> wrote:Simen kjaeraas wrote:The problem of D's lambda syntax is it is optimized for longer functions. Usually, the delegates I write are one line long. I cannot see that this syntax collides with anything at the moment, but feel free to enlighten me: { => 4; } { a => 2*a; } { a, b => a>b; } { => @ + @; } // turns into { a, b => a + b; }If size and simplicity of typing are critical, are those really better than: "a>b" ?No. But often, you want to call a function in a lambda, in which case the string version croaks.I'm not sure about the "often" part. For me, string lambdas do often suffice. When it doesn't, I use a lambda. D's syntax for lambdas is not syntactically heavy at all: (a, b) { return a + b; } The proposed alternative gravitates around (a, b) -> { a + b }
I never proposed that exact syntax, I don't think anyone else did either. I think just one person mentioned "->". This is the syntax I've proposed:
foo(3 * 4); // lazy argument/delegate foo(a => a * 3); foo(a, b => a * b); // or if not possible: foo((a, b) => a * b);
So this discussion concerns a niche between short lambdas that can be expressed as strings and lambdas for which the actual word "return" is too much to type. In fact we're looking at the difference between "return " + ";" and " -> ". Four characters.
No, you also added the {} characters.
If the new syntax would be executed to perfection, to what extent would that improve your use of D? To what extent would it make the language more powerful? To what extent does it allow to do things you otherwise wouldn't be able to?
Nothing, but there are a lot of things you can say the same about. I've also got the impression that you are pushing for a more functional approach of coding and for that a short, good and working lambda syntax is necessary.
Equally importantly, where is this four-characters saver on the radar compared to fixing const's issues, discussing tail const, completing and then improving 64-bit support, fixing important bugs, or even adding the lambda lowering that was discussed earlier in this thread to be promptly forgotten?
If this isn't a very quick implementation this would low on the priority list. I would like to have the lambda lowering as well :)
Also, it is not always possible to pass the lambda by template alias parameter, in which case the string version is right out the window.unaryFunc!"a + b"As for functions taking a delegate, the {=>@+@;} syntax will not work with overloading or template functions (nor will the other syntaxen that elides types). It could also be that functions taking delegates are or should be rare, and thus not worth optimizing for.I have no idea what {=>@+@;} does - it looks like a wrong paste from an early dialect of Perl to me. I have difficulty picturing someone who finds "a+b" or q{a+b} ugly but some other syntaxes discussed here palatable. Andrei
That syntax is just ugly. -- /Jacob Carlborg
