Max File Size
While doing some refactoring work on solution from this guy1,
I realized a pretty trivial thing about Manod method >>=
.
Take a look at its definition:
Prelude> :t (>>=) (>>=) :: (Monad m) => m a -> (a -> m b) -> m b
Both a
and b
ought to be some Monadic type! In other words, all
computation glued together by >>=
have same Manodic type.
It is really straightforward however I did not have that in mind.
Since I did want to define a function take a String
and return a list
of String
while its implementation has several computations that
return IO type. Obviously the function failed to compiled. Therefore I
changed it to return IO [String]
.
-- FilePath is from package System.IO and it is synonyms of String getFilesInDir :: FilePath -> IO [FilePath] getFilesInDir inp = do isDir <- doesDirectoryExist inp files <- if isDir then (do names <- getDirectoryContents inp forM [ inp </> x | x <- names, isNotSpecialDir x ] getFilesInDir) else return [[inp]] return $ concat files
PS:
- Full source code here2 which is cool as give me several suggestions.
- Actually it is possible to have multiple Monad in one
do
levarage Monad Transformers.