2008/12/26 Galchin, Vasili
<vigalchin@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