On Fri, 1 Feb 2008, Cale Gibbard wrote: > Hello, > > Today on #haskell, resiak was asking about a clean way to write the > function which allocates an array of CStrings using withCString and > withArray0 to produce a new with* style function. I came up with the > following: > > nest :: [(r -> a) -> a] -> ([r] -> a) -> a > nest xs = runCont (sequence (map Cont xs)) > > withCStringArray0 :: [String] -> (Ptr CString -> IO a) -> IO a > withCStringArray0 strings act = nest (map withCString strings) > (\rs -> withArray0 nullPtr rs act) > > Originally, I'd written nest without using the Cont monad, which was a > bit of a mess by comparison, then noticed that its type was quite > suggestive. > > Clearly, it would be more generally useful whenever you have a bunch > of with-style functions for managing the allocation of resources, and > would like to turn them into a single with-style function providing a > list of the acquired resources.
Nice idea. Could serve as an explanation what the Cont monad is good for. What about uploading it to the Wiki Category:Idioms ? _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
