On Saturday 13 August 2011, 20:04:57, Dennis Raddle wrote:
Can someone suggest an elegant way to write the following?
fn :: [Maybe Float] -> Maybe Float
in which, if the input list has all Nothing, then the result is Nothing if the input list has one or more Just x, then the result is Just x (in which the x is picked arbitrarily, could be the first one or last one)
import Control.Monad fn = msum (or, with only imports from Data.Maybe: listToMaybe . catMaybes)
I have something like
import Data.Maybe fn list = case catMaybes list of [] -> Nothing [x:_] -> fromJust x
Next, an augmentation of this idea (or similar idea).
fn2 :: [Maybe Float] -> Map Int Float
When a Just x appears at position n in the list, then put (key=n, value=x) into the map.
I have:
import qualified Data.Map as M f2 list = M.fromList [(n,x) | (n,Just x) <- zip [0..] list]
That's fine.