Good point. Happily I improved the error message a couple of weeks ago, so it'll be better in the next release Simon | -----Original Message----- | From: haskell-cafe-bounces@haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Daniel Fischer | Sent: 08 February 2008 22:24 | To: Ben Franksen; haskell-cafe@haskell.org | Subject: Re: [Haskell-cafe] Re: problem with collection (container) class | | Am Freitag, 8. Februar 2008 22:14 schrieb Ben Franksen: | > If it's a bug then it is probably in 6.6.1 too, it just gets hidden by the | > fact that in 6.6.1 the -fglasgow-exts extensions cannot be activated | > separately. If you enable one of them, you get them all. | > | Thanks for the info, didn't know that. | | The problem was the error message, which didn't mention that each type | variable may appear only once in an instance head, which I had temporarily | forgotten. Then the message | | Leandro.hs:32:0: | Illegal instance declaration for `Container (Abb a b) a b' | (All instance types must be of the form (T a1 ... an) | where a1 ... an are distinct type *variables* | Use -XFlexibleInstances if you want to disable this.) | In the instance declaration for `Container (Abb a b) a b' | | looks rather confusing :) | | > Cheers | > Ben | > | Cheers, | Daniel | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe@haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe