On Thu, Dec 15, 2011 at 5:33 PM, Sean Leather <span dir="ltr">&lt;<a href="mailto:leather@cs.uu.nl" target="_blank">leather@cs.uu.nl</a>&gt;</span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">

On Thu, Dec 15, 2011 at 11:07, Niklas Broberg wrote:<br><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Envisioned: The function you ask for can definitely be written for haskell-src-exts, which I know you are currently using. I just need to complete my type checker for haskell-src-exts first. Which is not a small task, but one that has been started.</blockquote>



<div><br></div><div>That&#39;s good to know! I presume it&#39;s something like Haskell98 to start with? I&#39;d be even more impressed (and possibly also concerned for your health) if you were going to tackle all of the extensions!</div>



</div></blockquote><div><br></div><div>Actually, no. Starting with Haskell98 would just lead to great pains later on, since many of the extensions require very invasive changes compared to a H98 checker. My starting point has been to identify the core structural and algorithmical requirements for a type checker that would indeed tackle &quot;all&quot; of the extensions.</div>

<div><br></div><div>My current checker (which I wouldn&#39;t even call half-complete) is based on a merge of the algorithms discussed in [1] and [2]. Between the two, they give, on the one hand, the bidirectional inference needed to handle arbitrary-rank types, and, on the other hand, the power of local assumptions needed to handle GADTs and type families.</div>
<div><br></div><div>I thank you for your concerns for my health. However, I assure you they are quite misplaced. Typing Haskell-with-extensions in Haskell is not only a far smaller beast than what it&#39;s made out to be, when walking in the well-documented footsteps of giants. It is also lots of fun. :-)</div>
<div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div class="gmail_quote"><div>I&#39;ve been trying to find a student to write a haskell-src-exts type checker for me. It should use a particular kind of mechanism though, using constraints similar to [1]. Then, I want to adapt that to do transformations. What approach are you using? Maybe I can somehow steal your work... ;)<br>
</div></div></blockquote><div><br></div><div>As you note from my starting references, I&#39;m using the same approach and base algorithms as GHC does. I looked at some alternatives briefly, including the work you reference, but I discarded them all since none of them had support for everything I wanted to cover. In particular, it is not at all clear how these systems would merge with bi-directional inference or local assumptions. Tackling *that* problem would be a large and very interesting research topic I&#39;m sure, but not one I have time to dig into at the current time. Indeed, the feasibility of my project (and thus the sanctity of my health) relies very heavily on the &quot;footsteps-of-giants&quot; factor...<br>
</div><div><br></div><div>So as not to give anyone false hopes, I should point out that I currently have next to no time at all to devote to this, and the project has been dormant since August. I&#39;ll return to it for sure, but at the moment cannot tell when.</div>
<div><br></div><div>Cheers,</div><div><br></div><div>/Niklas</div><div><br></div><div>[1] S. Peyton Jones, D. Vytiniotis, S. Weirich, and M. Shields. Practical type inference for arbitrary-rank types.<br></div><div>[2] D. Vytiniotis, S. Peyton Jones, T. Schrijvers, M. Sulzmann. OutsideIn(X) – Modular type inference with local assumptions<br>
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