Re: [Haskell-cafe] Type wildcards

Hi, On Tue, Dec 16, 2008 at 05:26:00PM +0200, Eyal Lotem wrote:

Martin Foster (aka. EvilTerran) suggested an interesting idea, and I decided it was too nice to ignore/be forgotten inside Martin's head... So I'd like to try and suggest it.

Type wildcards that allow partially specifying types, e.g:

f :: _ -> String f x = show x

This will instruct the type-inferrer to "fill out" the wild-card part only (e.g: Show a => a).

What you are describing is (an instance of) the "some" operator. For example, see http://research.microsoft.com/en-us/um/people/daan/download/papers/hmf.pdf Section 5.1, "Partial annotations". And yes, I agree, they are useful :) Edsko