Extracting ByteString from IO context?

Question

I have a function that makes a http request, I need to access the returned byte string. However, the monadic function I have doesn't seem to be able to return the ByteString separated from its IO.

See below:

executeRequest :: IO LAZ.ByteString
executeRequest = do
   response <- simpleHttp "http://www.bbc.co.uk"
   return (response)

html = executeRequest

extractBytesFromIO :: IO LAZ.ByteString -> LAZ.ByteString
extractBytesFromIO html = do
    bytes <- html
    bytes

The above won't compile, with an error:

Couldn't match expected type ‘LAZ.ByteString’ with actual type ‘IO b0’

I need to bring the ByteString out of the local scope of the function, so the below will not work:

html - executeRequest

extractBytesFromIO :: IO LAZ.ByteString
extractBytesFromIO = do
   bytes <- html
   let doStuff = //do stuff with bytes
   html

Any suggestions on how extractBytesFromIO can return the ByteString without the IO context?

If this were possible then we wouldn't need an `IO` monad in the first place. — leftaroundabout, Oct 08 '16 at 18:13
You can "bring it out of the local scope of the function," it's just that the function you bring it into has to also be in the IO monad. — Louis Wasserman, Oct 08 '16 at 20:05

Extracting ByteString from IO context?

0 Answers0