Hello,

I have a small piece of code that does not compile and I'm having trouble figuring out why.

Here is the relevant snippet:

readChunks :: Handle -> [String] -> IO [String]

readChunks handle accum = do

  chunk <- readHeaderChunk handle

  if isLast chunk

    then return (accum ++ chunk)

    else return (readChunks handle (accum ++ chunk))

isLast :: [String] -> Bool

readHeaderChunk :: Handle -> IO [String]

And here is the single compiler error:

hacks.hs:48:18:

    Couldn't match expected type `[String]'

                with actual type `IO [String]'

    In the return type of a call of `readChunks'

    In the first argument of `return', namely

      `(readChunks handle (accum ++ chunk))'

    In the expression: return (readChunks handle (accum ++ chunk))

What I'm most confused about is that chunk is passed to isLast as a [String] with no compiler error but cannot be passed to accum ++ chunk that way. Or so it seems. Can someone she some light on this? Thanks.

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