Re: A type checker plugin for row types

Thank you Matthew! I very much appreciate this kind of feedback. 1) I've updated the (bulk of the) wiki page to match the github repo just now. In particular, the "Elm" example lives here https://github.com/nfrisby/coxswain/blob/master/sculls/Elm.hs, so I just copied its most recent version onto the wiki. (The delta was the "off-by-one" `Short` constraints, right?) 2) I absolutely agree about -dcore-lint. I wrongly had it in my head that I needed a DEBUG build. See https://github.com/nfrisby/coxswain/issues/3#issuecomment-330266479 3) Awesome! I'll add a link to the README. Thanks again. -Nick On Mon, Sep 18, 2017 at 4:11 AM Matthew Pickering < matthewtpickering@gmail.com> wrote:

Hi Nicolas, I briefly tried out the plugin this morning and have a few comments.

1. The example file on the wiki page fails to compile. I needed to modify two of the constraints on `getName` and `getPos` to get it to work.

2. I was inspecting how well the compiler optimises your representation and came across from very strange core that I didn't understand.

https://gist.github.com/mpickering/6ec5501400e103d64284701d7537f223

Notice how there is a case on a lambda which binds an unused kind variable. But I can't understand how this works at all as I can't see where the lambda is applied.

3. Running -dcore-lint on the example file quickly complains. I think making sure that core-lint passes can be quite an important sanity check, is a fundamental reason which makes core lint work poorly with type checker plugins? If there is then we should perhaps fix this.

I also packaged up the project for nix if that is useful to anyone else.

https://gist.github.com/2a4b2fa25351bd900052d955a00ace6a

Matt

On Sat, Sep 16, 2017 at 11:00 PM, Nicolas Frisby wrote:

...

If you'd like to see how exactly the plugin manipulates constraints, I suggest using the `summarize` and `trace` options that are discussed here:

https://ghc.haskell.org/trac/ghc/wiki/Plugins/TypeChecker/RowTypes/Coxswain#...

...

Also, the `sculls/Examples.hs` and `sculls/Elm.hs` files contain my only test cases involving records and variants. Also see

`coxswain/test/README`.

...

I'm kind of spent from rushing towards this "release", so I might be a

...

less productive for a while. But I'll be generally responsive about it if others are spending time on it.

In particular: any advice for how to share the generated Haddock documentation without uploading to Hackage/Stackage?

And thanks to all for responding to my questions. I'll have to think harder about the answers given. At least for Derived constraints, in

bit particular, I

...

still don't think we have all of the relevant information in one place. For example, I recalling thinking that I was seeing some Derived constraints that seemed to arise from the unifier "giving up" on a complicated equality and emitting a Given equality instead, and nobody mentioned that in their answers here. I'll try to suss out a repro of that exactly.

Thanks. -Nick

On Sat, Sep 16, 2017 at 2:27 PM Nicolas Frisby

wrote:

...

I've uploaded the code to GitHub.

https://github.com/nfrisby/coxswain

I went with a BSD3 licence.

It's still very much a work in progress, so I only recommend using it

for

...

experimentation for now.

Thanks. -Nick

On Sun, Sep 10, 2017 at 3:24 PM Nicolas Frisby < nicolas.frisby@gmail.com> wrote:

...

Hi all. I've been spending my free time for the last couple months on a type checker plugin for row types. The free time waxes and wanes;

sending an

...

email like this one was my primary goal for the past couple weeks.

At the very least, I hoped this project would let me finally get some hands on experience with OutsideIn. And I definitely have. But I've also made more progress than I anticipated, and I think the plugin is starting to have legs!

I haven't uploaded the code yet to github -- it's not quite ready to share. But I did do a write up on the dev wiki.

https://ghc.haskell.org/trac/ghc/wiki/Plugins/TypeChecker/RowTypes/Coxswain

...

I would really appreciate and questions, comments, and --- boy, oh boy --- answers.

I hope to upload within a week or so, and I'll update that wiki page

and

...

reply to this email when I do.

Thanks very much. -Nick

P.S. -- I've CC'd and BCC'd people who I anticipate would be specifically interested in this (e.g. plugins, row types, etc). Please feel free to forward to others that come to mind; I know some inboxes abjectly can't afford default list traffic.

P.P.S. -- One hold up for the upload is: which license? I intend to release under BSD3, mainly to match GHC since one ideal scenario would involve being packaged with/integrated into GHC. But my brief recent research suggests that the Apache license might be more conducive to eventual widespread adoption. If you'd be willing to advise or even just refer me to other write ups, please feel free to email me directly or to start a separate thread on a more appropriate distribution list (CC'ing me, please). Thanks again.

_______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs