Improve getPagePath

[ghost]

The problem

The definition of Main.getPagePath is dependant on the length of Main.checkDirs:

getPagePath :: String -> IO (Maybe FilePath)
getPagePath page = do
  homeDir <- getHomeDirectory
  let pageDir = homeDir </> tldrDirName </> "tldr" </> "pages"
      x@(f1:f2:f3:f4:[]) = map (\x -> pageDir </> x </> page <.> "md") checkDirs
#if MIN_VERSION_base(4,7,0)
  f1' <- pageExists f1
  f2' <- pageExists f2
  f3' <- pageExists f3
  f4' <- pageExists f4
  return $ f1' <|> f2' <|> f3' <|> f4'
#else
  pageExists f1 <|> pageExists f2 <|> pageExists f3 <|> pageExists f4
#endif

This over complicates the process of adding new directories to Main.checkDirs.

The solution

Modify Main.getPagePath's definition to take advantage of Control.Monad's utilities. The result is:

getPagePath :: String -> IO (Maybe FilePath)
getPagePath page = do
  homeDir <- getHomeDirectory
  let pageDir = homeDir </> tldrDirName </> "tldr" </> "pages"
      paths = map (\x -> pageDir </> x </> page <.> "md") checkDirs
  foldr (<|>) Nothing <$> mapM pageExists paths

NOTE: I also disabled the CPP language extension, as, Main.getPagePath was the only function dependant CPP.

Status

This solution successfully compiles and runs on my Ubuntu 18.04.1 machine, with stack 1.7.1.

[psibi]

@Kove-W-O-Salter Thanks! I think you can use foldr1 to make it more simplified ?

[ghost]

Yes, that would be very readable. The only thing is that it will fail if checkDirs is []. Do you want me to change it?

[psibi]

Do you want me to change it?

Yes, checkDirs here will be always non empty.

[ghost]

Finished. I've changed the definition of getPagePath to:

getPagePath :: String -> IO (Maybe FilePath)
getPagePath page = do
  homeDir <- getHomeDirectory
  let pageDir = homeDir </> tldrDirName </> "tldr" </> "pages"
      paths = map (\x -> pageDir </> x </> page <.> "md") checkDirs
  foldr1 (<|>) <$> mapM pageExists paths

[psibi]

Thanks!

[ghost]

Thank you :smile:.