Re: [Haskell-cafe] Lifting a value into a DataKind

I fear, though, that you'll need a big hammer to be able to do what you want. Could you draw out your example a bit, and then we can see what the smaller hammer might look like. Richard

On Feb 7, 2017, at 10:32 PM, Ivan Lazar Miljenovic wrote:

Thanks for the suggestion; I think singletons is a bit of a large hammer for a small bit of extra functionality I was thinking of adding though (especially with people needing to use TH to make their datatypes instances of SingI as well).

On 8 February 2017 at 12:55, Richard Eisenberg wrote:

...

The singletons library's `toSing` (or `withSing`) may be what you want. Note that if you use Proxy, you won't be able to make any runtime decisions on the choice of `b`.

Richard

...

On Feb 7, 2017, at 6:55 PM, Ivan Lazar Miljenovic wrote:

Is it possible to automatically lift an arbitrary value into a type? i.e. I'm after a function of type `a -> Proxy (b :: a)`.

More specifically, I'm wanting to be able to write a function that can convert an Enum (e.g. Bool or Ord) into such a Proxy, so I can actually write a function that looks like: `a -> (forall b. Proxy (b :: a) -> r) -> r` and use the `a` type as a selector value (to e.g. choose between type class instances).

-- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com http://IvanMiljenovic.wordpress.com _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

-- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com http://IvanMiljenovic.wordpress.com