Re: [Haskell-cafe] coerce (safe!)
* Krzysztof Skrzętnicki [EMAIL PROTECTED] [2008-03-02 01:21:42+0100] Well, it is simply coerce :: a - b coerce _ = undefined so coerce is simply empty function. But still, it is possible to write a function of type (a-b). Well, possibly I didn't write anything particularly new, but please excuse me for I'm still in sort of a shock after I've discovered it. Also there's nice possibility of defining Maybe a without ADT. type Maybe a = (a, Bool) just x = (x, True) nothing = (undefined, False) -- Roman I. Cheplyaka :: http://ro-che.info/ ...being in love is totally punk rock... signature.asc Description: Digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] coerce (safe!)
2008/3/2 Roman Cheplyaka [EMAIL PROTECTED]: * Krzysztof Skrzętnicki [EMAIL PROTECTED] [2008-03-02 01:21:42+0100] Well, it is simply coerce :: a - b coerce _ = undefined so coerce is simply empty function. But still, it is possible to write a function of type (a-b). Well, possibly I didn't write anything particularly new, but please excuse me for I'm still in sort of a shock after I've discovered it. Also there's nice possibility of defining Maybe a without ADT. type Maybe a = (a, Bool) just x = (x, True) nothing = (undefined, False) That's a hack. This is my favorite: type Maybe a = forall b. (a - b) - b - b just x = \j n - j x nothing = \j n - n Luke ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] coerce (safe!)
On 03/03/2008, at 8:30 AM, Luke Palmer wrote: 2008/3/2 Roman Cheplyaka [EMAIL PROTECTED]: * Krzysztof Skrzętnicki [EMAIL PROTECTED] [2008-03-02 01:21:42 +0100] Well, it is simply coerce :: a - b coerce _ = undefined so coerce is simply empty function. But still, it is possible to write a function of type (a-b). Well, possibly I didn't write anything particularly new, but please excuse me for I'm still in sort of a shock after I've discovered it. Also there's nice possibility of defining Maybe a without ADT. type Maybe a = (a, Bool) just x = (x, True) nothing = (undefined, False) That's a hack. This is my favorite: type Maybe a = forall b. (a - b) - b - b just x = \j n - j x nothing = \j n - n For something slightly different, I've always enjoyed lists (or integer indexed structures) as functions: type List a = Integer - Maybe a You've got to watch out for non-contiguous lists. It's a good challenge to write head, tail, nil and cons for this type. Then write conversions to/ from normal lists. Bernie.___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] coerce (safe!)
Well, it is simply coerce :: a - b coerce _ = undefined so coerce is simply empty function. But still, it is possible to write a function of type (a-b). Well, possibly I didn't write anything particularly new, but please excuse me for I'm still in sort of a shock after I've discovered it. Yet this function reminds me how little I know so I have a question for you. I didn't took any lectures in Category Theory (for I'm still just a student, and I won't for there are none in my institute), but are there any good (e)books you would recommend for a (future) computer scientist? Regards Christopher Skrzętnicki ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] coerce (safe!)
On 2 mar 2008, at 01.21, Krzysztof Skrzętnicki wrote: Well, it is simply coerce :: a - b coerce _ = undefined so coerce is simply empty function. But still, it is possible to write a function of type (a-b). Well, possibly I didn't write anything particularly new, but please excuse me for I'm still in sort of a shock after I've discovered it. Yet this function reminds me how little I know so I have a question for you. I didn't took any lectures in Category Theory (for I'm still just a student, and I won't for there are none in my institute), but are there any good (e)books you would recommend for a (future) computer scientist? For your particular problem you might want to start with this thread (and the linked paper): http://lambda-the-ultimate.org/node/2003 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
