Re: [Vala] Proposal for an improved delegate/lambda handling

["Sam Liddicott" <sam liddicott com>]

I like any method that allows the callback block to acess all variables from the original scope and also allows execution of the callback to fall-through into the original scope at the end of the callback block; implying that the whole function must be generated with labda-style local vars.

Sam

---

From: Ali Sabil <ali sabil gmail com>
Sent: 19 October 2008 11:31
To: Christian Hergert <christian hergert gmail com>
Cc: Vala Mailing list <vala-list gnome org>
Subject: Re: [Vala] Proposal for an improved delegate/lambda handling

Here is another set of proposed syntaxes, so that the post_request() looks like this:

client.post_request("GET ...") {
    debug ("Got Response: %s", response);
} {
    debug ("Got error: %s", error);
}

Another possible syntax would be:

client.post_request("GET ...") {
    (response) => {
        debug ("Got response %s", response);
    }
}

which in the case of a callback+errback would look like:

client.post_request("GET ...") {
    (response) => {
        debug ("Got Response %s", response)
    }
    (error) => {
        debug ("Got error %s", error);
    }
}

This 2nd syntax is actually inspired from Scala. Scala supports currying, as well as optional parentheses for parameter passing,and the ability to substitute parentheses for curly brackets in some place. This set of feature combined together allow building methods and functions that look and feel like control structure. (At least that's what I understood during a short trip to the Scala world).

Thanks for all your feedback.

--
Ali

On Sun, Oct 19, 2008 at 2:00 AM, Christian Hergert <christian hergert gmail com> wrote:

I like it. Might get confusing if someone wanted to mix direct
delegates and anonymous ones though.

-- Christian

On Sat, Oct 18, 2008 at 4:14 PM, Yu Feng <rainwoodman gmail com> wrote:
> On Sat, 2008-10-18 at 22:57 +0200, Ali Sabil wrote:
>> Hi all,
>>
>> I would like to start a discussion about a small syntactic sugar
>> addition to Vala, that would in my opinion slightly improve the
>> situation with asynchronous code. The following code sample should be
>> self explanatory about my proposal:
>>
>> delegate bool HttpResponseCallback (string response);
>>
>> public class HttpClient : Object {
>>     public void post_request (string request, HttpResponseCallback cb)
>> {
>>         cb ("Hello world");
>>     }
>> }
>>
>> // Current State
>> var client = new HttpClient ();
>> client.post_request("GET ....",  (response) => {
>>         debug ("got response %s", response);
>>         return true;
>>     }
>> );
>>

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