Re: [Haskell-cafe] Hello and type-level SKI

On Fri, 12 Sep 2014, Tikhon Jelvis wrote:

Note how the provided code enables a bunch of language extensions, most notably UndecidableInstances. (Yep, that's exactly what it sounds like!)

It's quite far removed from standard Haskell or full type inference.

Yes. One thing that I now know is that, to date, there is a clean separation of estimation of the type of a function from the next stage of the GHC pipeline. In particular you cannot see in the Core code for the function the effect of the extensions, except possibly, whether or not any code is produced. I say "know", but all I have done is look at the high level explanations. I have not looked at any compiler code. So my understanding is not good and likely to be largely mistaken. oo--JS.

On Sep 12, 2014 4:30 PM, "Brandon Allbery" wrote:

...

On Fri, Sep 12, 2014 at 7:25 PM, Jay Sulzberger wrote:

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But this is impossible! The type system of Haskell can be handled by a Hindley-Milner-Damas style type checker. Such a type checker always comes to a halt with a Yea or Nay answer. So one cannot get a simulation of the combinators S, K, I inside the Haskell type system.

What have I misunderstood? And, in case GHC really does now handle stuff beyond the HMD horizon, what does the New Core language look like?

Standard Haskell is (or was) H-M extended with typeclasses. GHC moved beyond that years ago; internally it's System Fw ( http://en.wikipedia.org/wiki/System_F#System_F.CF.89), and its Core language reflects this.

-- brandon s allbery kf8nh sine nomine associates allbery.b@gmail.com ballbery@sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net

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