Roland Lutz
Hi!
I'm trying to implement a source-sink type of pattern where there are a number of sinks, each connected to exactly one source, and a number of sources, each connected to zero or more sinks. The program consists of some modules, each defining their own sources and sinks. To illustrate this, here's what this would look like in C:
Hey Roland, So essentially you want a data structure for some kind of bipartite graph. The most haskelly way to do that would probably to define the graph to be simply define the Bipartite graph to be a pair of Maps, and define functions to add/delete nodes and edges to the graph that make sure that the two maps keep in sync. This would give you something like: import qualified Data.Map as M data MySource = MySource { sourceState :: String , % and any other data specific to sources } data MySink = MySink { sinkState :: String, % and whatever else sinks have} data BiGraph src snk = BiGraph { sourceToSinkMap :: M.Map src [snk] , sinkToSourceMap :: M.Map snk src } addEdge :: (src,snk) -> BiGraph src snk -> BiGraph src snk addEdge (src,snk) (BiGraph m1 m2) = BiGraph (M.update src (snk :) m1) (M.insert snk src m2) % make sure to check that snk % does not already occur in % m2 etc. you essentially get your 'sinksForSource' functions for free: sinksForSource :: src -> BiGraph src snk -> [snk] sinksForSource src = M.lookup src . sourceToSinkMap In this model you cannot direclty mix the sources and sinks from different modules. I.e. a 'BiGraph MySource MySink' cannot be used to also store a (MySecondSource,MySecondSink) pairs. If you do want that, you would need some wrapper type that distinguishes between the various 'MySink', 'MySecondSink', versions. Note that instead of building such a graph type yourself you might also just want to use some existing graph library out there (i.e. fgl or so). Hope this helps a bit. -- - Frank