abstraction

I find myself often writing code following the pattern: foo xs = map snd $ filter ((< 10).fst) $ zip xs [0..] bar ys = map snd $ sortBy (compare `on` fst) $ zip ys [0..] Now I want to abstract this away foo = indexesOf (filter (<10)) bar = indexesOf sort indexesOf :: ([a] -> [a]) -> [a] -> [Int] indexesOf f xs = map snd $ magick $ zip xs [0..] where magick = undefined How to perform the magick ? Your type signature won't work. You need to be able to give the passed function a list of tuples, which means that you either have to use higher-rank types to force it to be polymorphic, or explicitly

I am currently struggling with a java abstraction problem. I have something like this: public interface State { }; public interface Dynamics { getObservationChance(State state, Observation observation); }; class SpecialState implements State { }; enum SpecialObservation() { FREE, WALL, etc. } class SpecialDynamics implements Dynamics { getObservationChance(State state, Observation observation) { // state should be SpecialState, observation should be SpecialObservation! } }; class Main { Main(State state, Observation observation, Dynamics dynamics) { dynamics.getObservationChance(state,

Lately I've stumbled upon an error in a lib that used to work just fine, and I'll be damned if I can figure out where it is. The code sample is below, and I apologize for the debug stuff that's inside it, but I'm trying to get it to work. The problem is that $temp is an array with correct key (the name of the columns) but all the values are NULL. I think the problem lies in the call_user_func_array(array($query, 'bind_result'), $params); bit, but can't really wrap my head around it. public function fetchRows(){ error_reporting(E_ALL+E_NOTICE); $args = func_get_args(); $sql = array_shift($args)

When should you throw a custom exception? e.g. I have some code that connects to a server. The code that connects to the server throws an IOException when it fails to connect. In the context of the method it's called, this is fine. It's also fine in the network code. But as this represents not having a connection (and therefore not working) the exception goes all the way up to the ui. At this stage, an IOException is very ambigous. Something like NoConnectionException would be better. So, my question is: At what stage should you catch an exception to instead throw another (custom) exception

How to design classes involving collections of other classes? General Example: A Workspace contains number of Projects . A Project contains large number of Resources . Each Resource may contain large number of Files . So here the classes identified can be Workspace,Project,Resource and File. Workspace will have list of Project.Project will have list of Resources and Resource will have list of Files. Of course each class has its related settings. Now the basic questions are : a) Who creates and adds a class to a particular collection? Another class or the class containing the collection? b)

I may very well be approaching this in the wrong way, so please forgive me of my naiveté: In order to learn Clojure I've begun porting my OAuth client library for Python to Clojure. I'm doing this by wrapping clj-http much in the same way I wrap Python Requests in the Python library. This seems to be working pretty well so far and I'm really enjoying seeing the implementation come to life in Clojure. However I have run into a problem: I'm planning to support both OAuth 1.0 and 2.0 and have split the respective functions into two files: oauth1.clj and oauth2.clj. Now, each file should ideally