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 ke...@malde.org wrote: Casey Hawthorne cas...@istar.ca 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
[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
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 mag...@therning.org wrote: On Fri, Nov 20, 2009 at 1:57 PM, Victor Mateus Oliveira rhapso...@gmail.com 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
