Pierre-Etienne Meunier wrote:
This way :
do
times<-mapM PF.getFileStatus filenames >>= return.(map
PF.modificationTime)
Or also :
do
times<-mapM (PF.getFileStatus >>= (return.(PF.modificationTime)))
filenames
let sorted=...
I do not know exactly how ghc compiles the IO monad, but it seems to me that
the latter would allocate a little less.
FWIW, (a >>= (return . f)) == (liftM f a) ~= (fmap f a)
Where available, the fmap version is the most efficient. The liftM
function can be less efficient since it's defined generically (namely
with the bind/return definition above), whereas fmap can take advantage
of knowing the specific monad it's working on. But then, not everyone
defines Functor instances for their monads...
--
Live well,
~wren
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