Re: Haskell for non-Haskell's sake
Hi Hal (et al.) I am using it to write a compiler and interpretor for a quantum programming language, based on the semantics of the paper by Peter Selinger. (See http://quasar.mathstat.uottawa.ca/~selinger/papers.html#qpl for details on the semantics) On 29 Aug, Hal Daume III wrote: > Hi fellow Haskellers, > > If you use Haskell for a purpose *other than* one of those listed below, > I'd love to hear. I don't need a long report, anything from a simple "I > do" to a paragraph would be fine, and if you want to remain anonymous > that's fine, too. > > Purposes which I consider "Haskell for Haskell's sake" include: > > - writing Haskell compilers/interpreters > - developing libraries for Haskell > - writing Haskell debuggers, tracers, profilers or other tools > - more or less anything with matches /.*Haskell.*/, other than > /in Haskell$/ :) > -- Brett G. Giles Grad Student, University of Calgary Formal Methods, Category Theory, Semantics of Programming http://www.cpsc.ucalgary.ca/~gilesb mailto:[EMAIL PROTECTED] ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: Hash in Haskell
Typically, such functions are often used to implement mappings from something (such as a String) to something else. If that is what you want take a look at the type FiniteMap under the Data area of GHC and HUGS. It implements all the needed functionality without having to worry about creating a Hash for the keys. If you want if for some other reason, you would typically need to define a class such as: Class Hash where hash::a->Int and then implement it on your desired types. Strings are ususally somewhat easy to create a unique has value, other types will, naturally, depend on what is in them. On 16 Jun, Sergio Sebastián Giro wrote: > Hi, I need some function in Haskell to hash any value from any type to > Int. I guess that such a function needs to be a primitive, but I don't > found it in Hugs. Do you know how I can implement it or found it? > Thanks > Sergio > ___ > Haskell mailing list > [EMAIL PROTECTED] > http://www.haskell.org/mailman/listinfo/haskell -- Brett G. Giles Grad Student, University of Calgary Formal Methods, Category Theory, Semantics of Programming http://www.cpsc.ucalgary.ca/~gilesb mailto:[EMAIL PROTECTED] ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: Question About lists
Hi Cesar If you check the prelude, you will find the definition (something like): length::[a]->Int length= foldl' (\n _ -> n + 1) 0 and the definition of foldl' foldl' :: (a -> b -> a) -> a -> [b] -> a foldl' f a [] = a foldl' f a (x:xs) = (foldl' f $! f a x) xs Which also gives a linear complexity (O(n)) to length. Unless your representation of lists stores the length, you will pretty much always need linear time to find out the length as you have to count how many items there are. Alternatively, if getting the length is something you need to do a lot, consider creating your own datatype and corresponding class for inserts etc. that keeps the length on hand. This could allow O(1) length queries. On 30 Dec, Cesar Augusto Acosta Minoli wrote: > > Hello! I'm Working with Lists in Haskell, I´m a Beginner in Functional >Programming and I would like to know if there is a way to write a more efficient >function that return the length of a list, I wrote this one: > long :: [a]->Intlong >p = longitud p >0 > >where > longitud [] >s=s > longitud (x:xs) s=longitud xs (s+1) > but I think that it have a lineal grow O(n). > thanks! > > > > Add photos to your e-mail with >MSN 8. http://g.msn.com/8HMEEN/2021";>Get 3 months FREE*. > ___ > Haskell mailing list > [EMAIL PROTECTED] > http://www.haskell.org/mailman/listinfo/haskell -- Brett G. Giles Grad Student, University of Calgary Formal Methods, Category Theory, Semantics of Programming http://www.cpsc.ucalgary.ca/~gilesb mailto:[EMAIL PROTECTED] ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
