Re: [Haskell-cafe] How to do the "permutation and combination" thing?
Hi, Give a try to this library: http://hackage.haskell.org/package/permutation You can construct the combinations with list of indices and then apply it to your sets. []s Victor On Fri, Mar 12, 2010 at 5:16 AM, Ketil Malde wrote: > Casey Hawthorne writes: > >>> For example, I have this: >>>list1 = [a, b, c] >>>list2 = [d, e, f] >>>list3 = [g, h, i] > >> Think in abstract terms what you want to accomplish. > > A bit more specifically, let's say the input is a list of lists, and you > want to produce all combinations of drawing one element from each of the > input lists¹: > > perms :: [[a]] -> [[a]] > > You need to consider two cases, when the input is empty, and when the > input contains at least one list of elements: > > perms (l:ls) = ... > perms [] = ... > > The second case shouldn't be so hard. > > Now, if you pretend that 'perms' is already implemented, then you can > use it to generate all permutations for the tail of the input list. The > first case boils down to combining the first input list with all > permutations of the rest of the lists: > > perms (l:ls) = ... l ... perms ls > > Does this help? > > -k > > ¹ Using tuples is harder to generalize for length, but nicer typewise, > since you'd get something like 'perms :: ([a],[b],..[x]) -> [(a,b,..,x)] > -- > If I haven't seen further, it is by standing in the footprints of giants > ___ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- GNU/Linux user #446397 - http://counter.li.org ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Improved message for GHC "No instance for" Errors
Hi, I would like to propose a modification in the ghc message for "no instance for" errors. In the message, the ghc tells that there's no instance for the type you are using and it give you a hint that you can fix it adding a new instance for your type. But it don't tell me any instance alternative that already exists. So, if I don't know the correct type, I need to look at the documentation. At least for me, I get this message when I'm using the function in the wrong way or when I forget to specify the some function signature. It's quite rare the I want to add a new instance. Of course that it's not a problem to look at the documentation, but improving it can save a significant time and help the beginers to guess the error and how fix it. In C++ and Java, when I use g++ or javac and I make a wrong overloading, the compiler show me some alternatives. I think it help more than tell me to add a new overload to the function. It's possible to do it in ghc? I'm new haskell programmer and I enjoying a lot this language. []s Victor -- GNU/Linux user #446397 - http://counter.li.org ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Graph drawing library for Haskell
I'm looking for something more integrated with a gui library. The jgraph integrates with swing, so you can move, create, delete, have popup menus, select nodes, and so on. I haven't found yet.. If there isn't, I thinking in create one lib with wxHaskell using wxDC... But by now, I really prefer to use one existing library. []s Victor On Fri, Nov 20, 2009 at 12:00 PM, Magnus Therning wrote: > On Fri, Nov 20, 2009 at 1:57 PM, Victor Mateus Oliveira > wrote: >> Hi, >> >> Anyone knows a good library for graph diagram drawing? Or a haskell >> binding for one? >> Something like jgraph. http://www.jgraph.com/jgraph.html > > I usually turn to graphviz for my Haskell graphing needs. > > /M > > -- > Magnus Therning (OpenPGP: 0xAB4DFBA4) > magnus＠therning．org Jabber: magnus＠therning．org > http://therning.org/magnus identi.ca|twitter: magthe > -- GNU/Linux user #446397 - http://counter.li.org ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Graph drawing library for Haskell
Hi, Anyone knows a good library for graph diagram drawing? Or a haskell binding for one? Something like jgraph. http://www.jgraph.com/jgraph.html []s' Victor -- GNU/Linux user #446397 - http://counter.li.org ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
