Re: [Haskell-cafe] Function composition in run-time?
On Wed, Aug 24, 2011 at 04:35:42PM +0400, dokondr wrote: Hi, What is the Haskell way to compose functions in run-time? Depending on configuration parameters I need to be able to compose function in several ways without recompilation. When program starts it reads configuration parameters from a text file. For example, I have three functions, f1, f2, f3, each doing some string processing. I need to support two configurations of string processors : if param1 then sp = f1 . f2 . f3 else sp = f1 . f3 I'd like to avoid 'if' somehow and instead use some declarative way to specify code to run in external configuration file. In other words I need some easy tools to create mini DSLs without all the efforts usually involved with implementing full-blown DSL. A simple alternative to if would be: options = [ (foo, f1 . f2 . f3) , (bar, f1 . f3 )] and then lookup param options. I don't know if this is what you're looking for, though. regards, iustin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Function composition in run-time?
If your functions have the same type, then you can easily collect them in a data structure, say list, and fold that. For example: function :: String - (String - String) function f1 = f1 function f2 = f2 function f3 = f3 runAUserSpecifiedComposition :: String - F runAUserSpecifiedComposition = foldl (.) id . map function . words runAUserSpecifiedComposition f1 f2 f3 should be equal to (f1 . f2 . f3) now. On 24 August 2011 13:35, dokondr doko...@gmail.com wrote: Hi, What is the Haskell way to compose functions in run-time? Depending on configuration parameters I need to be able to compose function in several ways without recompilation. When program starts it reads configuration parameters from a text file. For example, I have three functions, f1, f2, f3, each doing some string processing. I need to support two configurations of string processors : if param1 then sp = f1 . f2 . f3 else sp = f1 . f3 I'd like to avoid 'if' somehow and instead use some declarative way to specify code to run in external configuration file. In other words I need some easy tools to create mini DSLs without all the efforts usually involved with implementing full-blown DSL. Thanks, Dmitri ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Function composition in run-time?
On Wed, Aug 24, 2011 at 4:44 PM, Iustin Pop ius...@google.com wrote: On Wed, Aug 24, 2011 at 04:35:42PM +0400, dokondr wrote: Hi, What is the Haskell way to compose functions in run-time? Depending on configuration parameters I need to be able to compose function in several ways without recompilation. A simple alternative to if would be: options = [ (foo, f1 . f2 . f3) , (bar, f1 . f3 )] and then lookup param options. I don't know if this is what you're looking for, though. Thanks! Yes, this is what I need - simple and easy. Yet, how function application will work in this case ? I mean after lookup returns me a composition ... need to check what type will it be. -- All the best, dokondr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Function composition in run-time?
On Wed, Aug 24, 2011 at 04:57:19PM +0400, dokondr wrote: On Wed, Aug 24, 2011 at 4:44 PM, Iustin Pop ius...@google.com wrote: On Wed, Aug 24, 2011 at 04:35:42PM +0400, dokondr wrote: Hi, What is the Haskell way to compose functions in run-time? Depending on configuration parameters I need to be able to compose function in several ways without recompilation. A simple alternative to if would be: options = [ (foo, f1 . f2 . f3) , (bar, f1 . f3 )] and then lookup param options. I don't know if this is what you're looking for, though. Thanks! Yes, this is what I need - simple and easy. Yet, how function application will work in this case ? I mean after lookup returns me a composition ... need to check what type will it be. Well, as with your 'if', all compositions must have the same type, since lists are homogeneous. regards, iustin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Function composition in run-time?
On Wed, Aug 24, 2011 at 4:52 PM, Arseniy Alekseyev arseniy.alekse...@gmail.com wrote: If your functions have the same type, then you can easily collect them in a data structure, say list, and fold that. For example: function :: String - (String - String) function f1 = f1 function f2 = f2 function f3 = f3 runAUserSpecifiedComposition :: String - F runAUserSpecifiedComposition = foldl (.) id . map function . words runAUserSpecifiedComposition f1 f2 f3 should be equal to (f1 . f2 . f3) now. This is a nice one, looks already like tiny DSL ) I think I've got the main idea - enumerate in my program all function compositions in some data structure for Haskell to compile, and the associate these with parameter values in external file. Thanks everybody! dokondr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Function composition in run-time?
dokondr doko...@gmail.com wrote: This is a nice one, looks already like tiny DSL ) I think I've got the main idea - enumerate in my program all function compositions in some data structure for Haskell to compile, and the associate these with parameter values in external file. In Haskell you get a not-even-too-tiny DSL for free for composing functions in arbitrary, dynamic ways. Hint: (a -) is a monad and (-) is an ArrowChoice and an ArrowApply. Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife = sex) http://ertes.de/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
