Haskell Bytestrings: How to pattern match?

Question

I\'m a Haskell newbie, and having a bit of trouble figuring out how to pattern match a ByteString. The [Char] version of my function looks like:

Answer 1

Just to address the error message you received and what it means:

Couldn't match expected type `BS.ByteString'
       against inferred type `[a]'
In the pattern: []
In the definition of `dropR': dropR [] = []

So the compiler expected your function to be of type: BS.ByteString -> BS.ByteString because you gave it that type in your signature. Yet it inferred (by looking at the body of your function) that the function is actually of type [a] -> [a]. There is a mismatch there so the compiler complains.

The trouble is you are thinking of (:) and [] as syntactic sugar, when they are actually just the constructors for the list type (which is VERY different from ByteString).