Haskell parser error in where clause

Question

I'm using EMR to move a folder from local file system to S3 in Spark using fs.moveFromLocalFile API. Everything works fine except a 0-byte file created by EMRFS with name _$folder$ for EVERY folder that is uploaded.

Is there any way to move folders without this dummy file creation for every folder? (other than manually deleting this file). Also, why is this dummy file created? I'm currently using s3:// protocol recommended by EMR team.

Solution

Your indentation was wrong and i think you can only have one where in there (i could be very well wrong. I'm not a haskell guy). There was also a argument missing for the call to rev (an empty list):

palindrome :: [a] -> [a]
palindrome xs = con xs rs
    where con a b = rev (rev a []) b
          rs = rev xs []                       -- here
          rev [] rs = rs
          rev (x:xs) rs = rev xs (x:rs)

main = print (palindrome "hello")

Prints out:

"helloolleh"

I'm going to try to understand it now. Anyway, have fun!

Edit: Makes perfect sense to me now. I think that's the right version. For Haskell indentation rules, read Haskell Indentation

Comments

[Shruti Singh]

You are right, rs must start in same column as con in previous line. It is weird rule.

[Svante]

Not weird: same syntactic level -> same indentation

[Cubic]

I thought (++) was defined as (++) = flip $ foldr (:) - that's how I would've written it anyways.

[stevel]

it's trickier than you think. We need to (a) make sure that you can't mkdir under a file and (b) that empty directories exist when you do an ls. It's there in the expected semantics of an fs that mkdir path; ls path returns something successful. The FS clients do delete the marker files when things underneath are created