Changes to Typeable

Roman Leshchinskiy rl at
Sun Feb 12 03:18:39 CET 2012

On 12/02/2012, at 01:44, John Meacham wrote:

> I am not so sure, adding type applications to the language seems
> fairly radical and will change many aspects of the language. Something
> like Proxy that can be expressed in relatively vanilla haskell and
> some handy desugarings is much more attractive to me.
> With type apllications you end up with odd cases you need to figure
> out,  like forall a b. (a,b) and forall b a. (a,b) meaning different
> things maybe depending on the details of the impementation.... Also,
> it meshes with a core language based on type applications, like system
> F or jhc's PTS. However, it seems quite plausible that there are other
> ways of writing haskell compilers. Not that i am opposed to them, I
> just think they are way overkill for this situation and any solution
> based on them will be ghc-bound for a long time probably.

Type application doesn't necessarily have to tied to the forall syntax. You already suggest {:: T} as a shortcut for (Proxy :: Proxy T). Now suppose {T} is a shortcut for the type Proxy T and you could write:

class Typeable t where
  typeRep :: {t} -> TypeRep

... typeRep {::Int} ...

But now you don't need Proxy at all, although it's a perfectly valid desugaring.

I'm not necessarily suggesting the syntax above, just trying to point out that type application syntax might be bound to a specific type abstraction syntax.


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