Re: Changes to Typeable

In practice I've found that working with Tagged is a huge pain relative to working with Proxy. You usually need to use ScopedTypeVariables or do asTypeOf/asArgOf tricks that are far more complicated than they need to be. For reference you can compare the internals of reflection before when it used to use Tagged, and after I switched it to use Proxy. The Proxy version is much simpler. Tagged works well when you only need one tag and are going to use it for a lot of types. That really isn't the usecase with Typeable most of the time. -Edward On Fri, Feb 10, 2012 at 7:35 PM, Bas van Dijk wrote:

...

Would it be useful to make 'Proxy' an unboxed type itself? so

Proxy :: forall k . k -> #

This would statically ensure that no one accidentally passes ⊥ as a

On 11 February 2012 00:30, John Meacham wrote: parameter

...

or will get anything other than the unit 'Proxy' when trying to evaluate it. So the compiler can unconditionally elide the parameter at runtime. Pretty much exactly how State# gets dropped which has almost the same definition.

Or don't use an argument at all:

class Typeable t where typeRep :: Tagged t TypeRep

newtype Tagged s b = Tagged { unTagged :: b }

See:

http://hackage.haskell.org/packages/archive/tagged/0.2.3.1/doc/html/Data-Tag...

Bas

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