Re: [Haskell-cafe] ByteString typechecking issues....

Not in scope: `Data.ByteString.join' when Data.ByteString.join $ encode (buildHeader ss) -- ByteString -- [] (map encode (buildEntries (sequenceListExtract ss))) -- [ByteString] ?? Thanks, guys On Sat, Dec 27, 2008 at 3:13 AM, Eugene Kirpichov wrote:

I think Luke meant that you forgot to qualify the import for join, and the compiler guessed that you are meaning the monad one, thus the error.

2008/12/27 Galchin, Vasili :

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Hi Luke,

join :: ByteString -> [ByteString] -> ByteString ???

Vasili

On Sat, Dec 27, 2008 at 1:58 AM, Luke Palmer wrote:

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2008/12/26 Galchin, Vasili

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Hello,

I have a ByteString -> [ByteString] -> ByteString situation, i.e. concatenation .....

-- marshall into ByteString representation join (encode (buildHeader ss)) -- ByteString (map encode (buildEntries (sequenceListExtract ss))) -- [ByteString]

I get the following typecheck error which is vexing me ....

Couldn't match expected type `t -> t -> B.ByteString' against inferred type `B.ByteString'

???

join is not a function in Data.ByteString. By the error I'm guessing you're getting the join from Control.Monad, instantiated to (->). You are looking for "concat"; i.e. concat $ encode (buildHeader ss) : -- ByteString map encode (buildEntries (sequenceListExtract ss)) -- [ByteString]

(Control.Monad.join does end up meaning"concat" when working on lists of lists, but it does not generalize to lists of other things). Luke

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