[Haskell-cafe] New type of ($) operator in GHC 8.0 is problematic

Edward Kmett ekmett at gmail.com
Sat Feb 6 17:12:47 UTC 2016

As you dig deeper into Haskell you'll eventually need to understand what
these mean to reason about anything beyond first order code.

The primitives that GHC uses to implement arrays, references and the like
live in #. We then wrap them in something in * before exposing them to the
user, but you can shave a level of indirection by knowing what lives in #
and what doesn't.

But even if you never care about #, Int, Double, etc. are of kind *,
Functors are of kind * -> *, etc. so to talk about the type of types at all
you need to be able to talk about these concepts at all with any rigor, and
to understand why Maybe Maybe isn't a thing.

On Sat, Feb 6, 2016 at 8:15 AM, Imants Cekusins <imantc at gmail.com> wrote:

> Thank you Takenobu
> the links are useful, yes.
> Is knowledge of these terms necessary to program or are these terms of
> most interest to compiler developers?
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