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You can reach the person managing the list at beginners-ow...@haskell.org When replying, please edit your Subject line so it is more specific than "Re: Contents of Beginners digest..." Today's Topics: 1. Re: User-defined polymorphic data type: heterogeneous list? (Ertugrul Soeylemez) 2. Re: safetail problem (Thomas) 3. Re: User-defined polymorphic data type: heterogeneous list? (Ertugrul Soeylemez) 4. Re: safetail problem (Roelof Wobben) ---------------------------------------------------------------------- Message: 1 Date: Wed, 13 Jul 2011 00:32:10 +0200 From: Ertugrul Soeylemez <e...@ertes.de> Subject: Re: [Haskell-beginners] User-defined polymorphic data type: heterogeneous list? To: beginners@haskell.org Message-ID: <20110713003210.5b6d3...@angst.streitmacht.eu> Content-Type: text/plain; charset=US-ASCII David McBride <dmcbr...@neondsl.com> wrote: > myList :: MyClass a => [a] > myList = [somefunction True, somefunction False] This is not a heterogenous list. The list elements would still have to have the same type. Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/ ------------------------------ Message: 2 Date: Wed, 13 Jul 2011 00:33:57 +0200 From: Thomas <hask...@phirho.com> Subject: Re: [Haskell-beginners] safetail problem To: beginners@haskell.org Message-ID: <4e1ccbd5.20...@phirho.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed On 12.07.2011 22:45, Roelof Wobben wrote: > Hello, > I use Programming in Haskell from Graham Hutton. > But I can't find anything in the first 4 chapters from that book why I must > use (0,x) en what that means. FWIW: chapter 4.4, page 33. Regards, Thomas ------------------------------ Message: 3 Date: Wed, 13 Jul 2011 00:39:02 +0200 From: Ertugrul Soeylemez <e...@ertes.de> Subject: Re: [Haskell-beginners] User-defined polymorphic data type: heterogeneous list? To: beginners@haskell.org Message-ID: <20110713003902.6cb97...@angst.streitmacht.eu> Content-Type: text/plain; charset=US-ASCII Arlen Cuss <cel...@sairyx.org> wrote: > As Mats pointed out, an existential quantification will let you define > your polymorphic element (and to quote Mats): > > > {-# LANGUAGE ExistentialQuantification #-} > > > > data HeteroElement = forall a. Element a > > > > list = [Element 1, Element 'a', Element True] > > The question is, what can you do with this list? You can't "show" it, > because there's no requirement on HeteroElement's "a" type of it > having a Show instance (adding 'deriving Show' to the data statement > will cause an error, as it cannot be done for all 'a'!). You can't > find out their types. Indeed, you can't do anything at all with an > Element, simply because there's no restriction placed on their > value. They could contain anything at all. This definition is indeed not very useful, but you can have something like the following: class Renderable a class Updatable a data GameObj = forall a. (Renderable a, Updatable a) => GameObj a list :: [GameObj] list = [ GameObj SpaceMarine, GameObj Zombie, GameObj BFG9000 ] Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/ ------------------------------ Message: 4 Date: Wed, 13 Jul 2011 07:07:11 +0000 From: Roelof Wobben <rwob...@hotmail.com> Subject: Re: [Haskell-beginners] safetail problem To: <beginners@haskell.org> Message-ID: <snt118-w24ba3edc552834fbeee15fae...@phx.gbl> Content-Type: text/plain; charset="iso-8859-1" Oke, I changed it to this : http://codepad.org/ROV4ASAB But still there are errors. Roelof ---------------------------------------- > Date: Wed, 13 Jul 2011 00:33:57 +0200 > From: hask...@phirho.com > To: beginners@haskell.org > Subject: Re: [Haskell-beginners] safetail problem > > On 12.07.2011 22:45, Roelof Wobben wrote: > > Hello, > > I use Programming in Haskell from Graham Hutton. > > But I can't find anything in the first 4 chapters from that book why I must > > use (0,x) en what that means. > > FWIW: chapter 4.4, page 33. > > Regards, > Thomas > > _______________________________________________ > Beginners mailing list > Beginners@haskell.org > http://www.haskell.org/mailman/listinfo/beginners > ------------------------------ _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners End of Beginners Digest, Vol 37, Issue 23 *****************************************