2008/12/26 Galchin, Vasili <vigalc...@gmail.com>
> 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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