ByteString typechecking issues....

Galchin, Vasili

27 Dec 2008 27 Dec '08

12:13 a.m.

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' ??? Thanks, Vasili

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Galchin, Vasili

27 Dec 27 Dec

2:44 a.m.

Hello, Using a strongly-typed language so should just have to check "domain" and "co-domain" of functions? Vasili On Fri, Dec 26, 2008 at 11:13 PM, Galchin, Vasili wrote:

...

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'

???

Thanks, Vasili

Luke Palmer

2:58 a.m.

2008/12/26 Galchin, Vasili

...

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

Galchin, Vasili

3:14 a.m.

Hi Luke, joinhttp://cvs.haskell.org/Hugs/pages/libraries/base/Data-ByteString.html#v%3Ajo...:: ByteStringhttp://cvs.haskell.org/Hugs/pages/libraries/base/Data-ByteString.html#t%3ABy...-> [ ByteStringhttp://cvs.haskell.org/Hugs/pages/libraries/base/Data-ByteString.html#t%3ABy...] -> ByteStringhttp://cvs.haskell.org/Hugs/pages/libraries/base/Data-ByteString.html#t%3ABy...??? Vasili On Sat, Dec 27, 2008 at 1:58 AM, Luke Palmer wrote:

...

2008/12/26 Galchin, Vasili

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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Galchin, Vasili
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