<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><div>On 21 Mar 2012, at 19:22, Garrett Smith wrote:</div><blockquote type="cite"><div><blockquote type="cite"><font class="Apple-style-span" color="#000000"><br></font></blockquote><br>This may come down to personal taste. I don't like having to dig<br>around in parse transform code to understand what my module looks<br>like.<br><br></div></blockquote><div><br></div><div>Neither do I - that's why I simply run 'escript `evm site`/parse_trans/ebin/parse_trans_pp.beam ebin/<target>.beam' over the generated beam to see what it looks like at source level. ;) </div><br><blockquote type="cite"><div>eunit is a great example. If you really love eunit, then I'm not going<br>to convince you :)<br><br></div></blockquote><div><br></div><div>Common test and PropEr do exactly the same thing. I'm not sure what you're expected testing frameworks to do instead!?</div><br><blockquote type="cite"><div><blockquote type="cite"><blockquote type="cite">- Hiding the client-server distinction in Erlang is a terrible disservice<br></blockquote></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">I agree with this wholeheartedly, but don't see what it has to do with code generation.<br></blockquote><br>If you consolidate both the client and server functions into one<br>function, you've obfuscated an important distinction.<br><br></div></blockquote><div><br></div><div>I never suggested doing that at all. Not that I mean to be prickly, as we're all part of the same community and whatnot, but nobody suggested separating both functions. What the OP suggested was that you could define the interface declaratively - e.g., without writing the code directly - and that was what I was responding to. As I mentioned later on, in this particular gen_server case I actually think your approach is probably cleaner and more appropriate, but it's good to separate these points and refine the discussion I think.</div><br><blockquote type="cite"><div><blockquote type="cite"><blockquote type="cite">IMO, e2 solves the problem of "too much boiler plate". It's really<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">easy and requires zero magic.<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">Here's a "gen_server" equivalent in e2:<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><a href="https://github.com/gar1t/e2v2/blob/master/examples/ping/src/ping_server.erl">https://github.com/gar1t/e2v2/blob/master/examples/ping/src/ping_server.erl</a><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">This is pretty cool though. :)<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite"><blockquote type="cite">You might object to the separation of "ping" and "handle_msg" -- it<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">appears to be just one function, so why break it up into two pieces?<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">The problem is that it's not one function -- it's definitely *two*<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">very separate pieces of code.<br></blockquote></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">Absolutely and a good point!<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">When you write a gen_server style module, you're writing code that<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">support client-server interactions. You have, in the same module, code<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">that is called by the "client" and code that is called by the<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">"server". If you don't grok this, you're missing the entire point of<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">this type of module.<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">Code that hides this difference -- e.g. a parse transform that gloms<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">the client and server functions into one -- is IMO a Really Bad Idea.<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">I don't necessarily agree with this, as the parse transform can be applied to a -spec which is potentially as intention revealing as a hand written function. I do take your point about them being two separate functions and perhaps in this particular case (for gen_server) you are actually correct and having two hand coded parts is actually better. I don't buy 'code-gen is bad' as a general argument (which perhaps you weren't going so far as to make anyway), and I do see your point in this instance.<br></blockquote><br>I'm certainly not arguing against code generation. I think Erlang's<br>parse transform scheme is *very* good -- flexible enough to enable<br>elegant solutions but with enough complexity to scare off casual "meta<br>programmers".<br><br>But -- I think there should be a very clear payoff for using a parse<br>transform. I don't think the discussion here, which is "boilerplate"<br>is a good application for that.<br><br></div></blockquote><div><br></div><div>I think it depends on how much boilerplate you're looking at. As an OCaml programmer I have seen a *lot* of work going into removing boilerplate code, and the same in Haskell (although there I am less experienced) and overall I think the payoff you're describing is a value judgement based on the negative impact of using code generation. Generated code is brittle - there's no two ways about it. But it doesn't prevent you from testing or documenting, nor does it have to make your code opaque and difficult to understand, so long as it is not overused - a sprinkle here and there rather than a bucket load.</div><br><blockquote type="cite"><div>A good example of a value-add parse transform IMO is modlib, which<br>lets you create mods for inets httpd withou causing your brain to<br>explode [1].<br><br><blockquote type="cite"><blockquote type="cite">As an example of how this client/server difference is important,<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">consider form validation in a web app. There are two places you can<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">run code to validate form input -- you can validate it in the browser<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">using JavaScript, or you can send the form data to the server. Web<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">developers may opt for browser validation to avoid the expense of<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">sending data to the server -- or they might prefer it on the server.<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">Either way, it's an important consideration.<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">This same dynamic applies to gen_server style modules. If you stick<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">with it, I think you'll appreciate the separateness of client and<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">server facing code.<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">As for the boilerplate, I couldn't agree with you more!<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">Garrett<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">P.S. I'm giving a talk on e2 at the SF Factory in a couple weeks,<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">where I'll get into this in more details. Also, the e2 docs and github<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">project are in slight disarray at the moment, but will be put in order<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">this weekend!<br></blockquote></blockquote><br>[1] <a href="https://github.com/gar1t/modlib">https://github.com/gar1t/modlib</a><br></div></blockquote></div><br></body></html>