CODEWITHSUNDEEP
haskellrecursionfold
Carbon
Carbon

Reputation: 3973

Turn recursion to fold?

I wrote this code that loops through the lines of a file handle and does an arbitrary action with it. I don't think it should need to be recursive - can I make it into a fold action?

Thanks!

processHandle :: Handle -> (String->IO ()) -> IO ()
processHandle h fn = do
                   eof <- hIsEOF h
                   if eof then
                     return ()
                    else do
                      myLine <- hGetLine h
                      fn myLine
                      processHandle h fn

Upvotes: 1

Views: 229

Answers (1)

leftaroundabout
leftaroundabout

Reputation: 120751

Manually working with handles is very eschewed in Haskell. It doesn't play well together with a functional programming style.

For a simple input processor like this, it's probably the best to just read the entire file as one (lazy) string, and process the lines of that:

processHandle h fn = mapM_ fn . lines =<< hgetContents h

Of course this can also be written as a fold, just look up the definition of mapM_.

Now, this lazy-IO approach doesn't work as well for many serious applications. If this isn't one huge file, then you may be good if you just read the file strictly with the Data.Text equivalent. Else, if you really need to read lines interleaved with the processing steps, better look into conduit.

Upvotes: 6

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