[Haskell-cafe] Hello and type-level SKI

[Jay Sulzberger]

On Fri, 12 Sep 2014, Brandon Allbery <allbery.b at gmail.com> wrote:

> On Fri, Sep 12, 2014 at 7:25 PM, Jay Sulzberger <jays at panix.com> wrote:
>
>> 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.

Thanks, Brandon!

OK, so the way one simulates, ridiculous word, a Turing machine
is to write code for a function in Haskell.  The (simulation of)
running of the Turing machine, if I understand correctly, is
Haskell's attempt to calculate a type for the function.
Specifically, the type inferencer's attempt.  I will look at the
implementation of S, K, and I, and try to figure out how this
works.

oo--JS.


>
> -- 
> brandon s allbery kf8nh                               sine nomine associates
> allbery.b at gmail.com                                  ballbery at sinenomine.net
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