[racket-dev] What is handle in racket?

I got it.

Thanks Ray!

- Joe

On 01/21/2011 05:12 AM, Jay McCarthy wrote:
> 2011/1/21 Insik Cho<iminsik at gmail.com>:
>> hi guys,
>>
>> I have used 'call/input-url' function frequently, whose definition is:
>>
>> (call/input-url URL connect handle) → any
>> URL : url?
>> connect : (url? . ->  . input-port?)
>> handle : (input-port? . ->  . any)
>>
>> I coded like:
>>
>> (define a-url (string->url "http://www.google.com"))
>> (call/input-url a-url get-pure-port (lambda (p) (display (read-bytes 1024
>> p))))
>>
>> Tired to type 'lambda' function, I extracted it like:
>>
>> (define a-url (string->url "http://www.google.com"))
>> (define (read-1024 p) (display (read-bytes 1024 p)))
>> (call/input-url a-url get-pure-port (read-1024 p))
> You are calling "read-1024" with the argument "p" which appears to be
> free in this program. You don't want to pass call/input-url the result
> of read-1024, you want to call it with read-1024 itself:
>
> (call/input-url a-url get-pure-port read-1024)
>
>> But, it generates errors.
>>
>> What's wrong?
>> The question is: what 'handle' means?
> 'handle' has no special meaning in Racket. This library just uses that name.
>
>> Is it like a callback function in C?
> You could imagine that it is a "callback" from call/input-url to your
> code to do something to the port before it closes it.
>
> Jay
>
>> Thanks in advance.
>>
>> - Joe
>>
>>
>>
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