On 6/4/07, Stefan O'Rear wrote:

On Mon, Jun 04, 2007 at 12:05:56PM -0700, David Fox wrote:

...

I created this file by simplifying an error I was getting from a program that uses the Javascript types. If you remove the type signatures for f1 and f2 it compiles, but how do I fix the error I get when I compile with the signatures?

module Main where

type CPS c a = (a -> c) -> c

class CNode a data TNode = TNode instance CNode TNode

m :: TNode -> TNode -> Bool m a b = f1 b a $ \_ -> True

f1 :: (CNode a, CNode b) => a -> b -> CPS c a f1 a b f = f2 a b $ \_ -> f a

f2 :: (CNode a, CNode b) => a -> b -> CPS c a f2 a b f = f1 a b $ \_ -> f a

This gives these messages:

yhc -linkcore Browser3.hs Compiling Main ( Browser3.hs ) -- during after type inference/checking Error: No default for Main.CNode at 16:1-16:29.(Id 215,[(Id 200,Id 250)]) Error: No default for Main.CNode at 16:1-16:29.(Id 214,[(Id 200,Id 251)]) Error: No default for Main.CNode at 13:1-13:29.(Id 220,[(Id 200,Id 248)]) Error: No default for Main.CNode at 13:1-13:29.(Id 219,[(Id 200,Id 249)])

You can replace the CNode/TNode and CPS declarations with this:

import DOM.Level1.Html import DOM.Level1.Dom import CPS

same result.

Works fine in both GHC and Hugs. I don't think this bug will be fixed, because the current typechecker is already on the chopping block (see Matthieu's SoC project). So just wait a few months, or help.

Stefan

Where do I see Matthieu's SoC project? I scanned the last six months of the YHC mailing list, maybe I missed it.

On 6/4/07, Stefan O'Rear wrote:

On Mon, Jun 04, 2007 at 04:12:46PM -0700, David Fox wrote:

...

On 6/4/07, Stefan O'Rear wrote:

...

On Mon, Jun 04, 2007 at 12:05:56PM -0700, David Fox wrote: Works fine in both GHC and Hugs. I don't think this bug will be fixed, because the current typechecker is already on the chopping block (see Matthieu's SoC project). So just wait a few months, or help.

Stefan

Where do I see Matthieu's SoC project? I scanned the last six months of the YHC mailing list, maybe I missed it.

http://code.google.com/soc/haskell/appinfo.html?csaid=AB859DA837B7BDCD

Stefan

What I was wondering is what those "No default for Main.CNode" messages would be expected to mean. Maybe if I could supply the default it claims is missing I could work around this problem. Presumably people are using type classes without constantly running into this problem.