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Re: with-url

From: Dmitry Gutov
Subject: Re: with-url
Date: Sat, 21 Jan 2017 23:26:07 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:51.0) Gecko/20100101 Thunderbird/51.0

On 21.01.2017 18:44, Lars Ingebrigtsen wrote:

Nope.  You should only signal an error if you have an error, and getting
a 404 isn't an error.

Whether 404 is an error or not, depends on an application. And I'm saying that as someone with a few years of experience writing web applications that do HTTP requests themselves.

Consider the case where an application calls a function foo (which implements some sort of abstraction layer), and the said function uses with-url.

If foo is supposed to be general purpose (used in different applications), it would have to handle errors in a general way, so that any of its callers could still handle any kinds of errors, without being a macro. I'd rather with-url (or its replacement) was an example of doing that already.

Something else I take an issue with, is with `with-url' being a
macro. :) That violates The First Rule of Macro Club.

Yes, the first rule is "use a macro when it makes sense".

Not really. And macros make sense the most when we add a control flow construct, or some sort of definition syntax for a new facility. Neither of which is really the case here.

You're basically joining a library function with a control flow construct together.

2) Basically require to use the newly-introduced threads for

Using the new threads is a trivial rewrite and doesn't affect the
signature of the macro.

It could simplify it, by allowing to treat asynchronous code like synchronous one.

Anyway, I think the best option here would be to just have an
:ignore-errors parameter to `with-url'.  In that case, the body will
just be evaluated if we get non-error response.

I'm rather more worried about being able to handle errors in an asynchronous fashion.

You could say 404 is not an error, but handling it in a similar way to all other "actual" errors like "can't resolve the hostname" and "connection timeout" can be pretty handy.

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