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http-client: Access response body of error responses
by Sevcsik András 12 Jul '15

12 Jul '15

Hi list, Is there any way to read the response body of an >=400 HTTP response with http-client? If the response is an error response, it throws a StatusCodeException [1], which only exposes the headers, not the whole Response value. However, CouchDB gives a response body for the error responses, describing the error, which I want to access. [1]: https://hackage.haskell.org/package/http-client-0.2.1.1/docs/Network-HTTP-C… Cheers -- Minden jót, Sevcsik András

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cabal install snap-server-0.9.5.1: At least the following dependencies are missing: attoparsec >=0.10 && <0.13 && ==0.13.0.1
by Stanislaw Findeisen 12 Jul '15

12 Jul '15

Hi Could anyone explain this to me, please? $ cabal install snap-server-0.9.5.1 Resolving dependencies... Configuring snap-server-0.9.5.1... cabal: At least the following dependencies are missing: attoparsec >=0.10 && <0.13 && ==0.13.0.1 cabal: Error: some packages failed to install: snap-server-0.9.5.1 failed during the configure step. The exception was: ExitFailure 1 Where does this unsatisfiable dependency come from? snap-server-0.9.5.1 seems to require just attoparsec (>=0.10 && <0.14): http://hackage.haskell.org/package/snap-server-0.9.5.1 . And attoparsec 0.13.0.1 is already installed: $ cabal list --installed attoparsec * attoparsec Synopsis: Fast combinator parsing for bytestrings and text Default available version: 0.13.0.1 Installed versions: 0.13.0.1 Homepage: https://github.com/bos/attoparsec License: BSD3 * attoparsec-enumerator Synopsis: Pass input from an enumerator to an Attoparsec parser. Default available version: 0.3.4 Installed versions: 0.3.4 Homepage: https://john-millikin.com/software/attoparsec-enumerator/ License: MIT I am trying to install hakyll 4.6.*, and snap-server seems to be one of the requirements. Hakyll 4.6.* is an old version but AFAIR I need that due to conflicting versions of containers. Thanks! -- http://people.eisenbits.com/~stf/ http://www.eisenbits.com/ OpenPGP: 9EC2 5620 2355 B1DC 4A8F 8C79 0EC7 C214 E5AE 3B4E

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Monad problem
by René Klačan 12 Jul '15

12 Jul '15

Hi all, I've been trying to create working example with "ig" https://hackage.haskell.org/package/ig-0.2.2 - library over instagram API and I am facing little monad problem. Can someone advise me please how to make this small piece of code work? {-# LANGUAGE OverloadedStrings #-} import Network.HTTP.Client import Instagram code = "xxx_some_code" redirectUrl = "http://localhost:9988/instagram/oauth2/callback" credentials = Credentials "xxx_some_api_id" "xxx_some_api_secret" main :: IO () main = do manager <- newManager defaultManagerSettings token <- runInstagramT credentials manager $ getUserAccessTokenURL2 redirectUrl code print token I am getting following error: src/Main.hs:14:9: No instance for (Control.Monad.Trans.Resource.Internal.MonadResource IO) arising from a use of ‘getUserAccessTokenURL2’ In the second argument of ‘($)’, namely ‘getUserAccessTokenURL2 redirectUrl code’ In a stmt of a 'do' block: token <- runInstagramT credentials manager $ getUserAccessTokenURL2 redirectUrl code In the expression: do { manager <- newManager defaultManagerSettings; token <- runInstagramT credentials manager $ getUserAccessTokenURL2 redirectUrl code; print token } Thanks Rene

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Fwd: cabal install snap-server-0.9.5.1: At least the following dependencies are missing: attoparsec >=0.10 && <0.13 && ==0.13.0.1
by Imants Cekusins 10 Jul '15

10 Jul '15

> There is also a stack tool, Thank you. It is very interesting. Why were new tools introduced instead of adding new functionality to cabal? A mix of packaging tools may lead to confusion.

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-fglasgow-exts in .cabal
by Imants Cekusins 09 Jul '15

09 Jul '15

How to specify defaultExtensions in cabal (1.22) file? e.g. -fglasgow-exts or TypeSynonymInstances ?

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Loch package builds?
by Imants Cekusins 07 Jul '15

07 Jul '15

Did anyone try to install loch package recently: https://wiki.haskell.org/Debugging#Source-located_errors This error comes up on install: Debug/Trace/Location.hs:70:8: Expecting one more argument to ‘C.Exception’ Expected a type, but ‘C.Exception’ has kind ‘* -> Constraint’ In the type signature for ‘ppr’: ppr :: C.Exception -> String Failed to install loch-0.2 cabal: Error: some packages failed to install: loch-0.2 failed during the building phase. The exception was: ExitFailure 1 ?

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case statement
by Imants Cekusins 07 Jul '15

07 Jul '15

interestingly, the below test fails. May I ask: If "case" a1 is not the same as "where" a1, what is its value? Why does x=1 match against a1? note: result1 indent is aligned with a1 on the previous line ------ test module TestCase where import Test.Hspec main::IO() main = hspec $ do describe "TestCase" $ do it "case 1 - pass" $ do result1 1 `shouldBe` "one" it "case 2 - fail" $ do result1 2 `shouldBe` "two" where a1 = 2 result1 x = case x of a1 -> "one" 2 -> "two"

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Defining an Instance of Ord
by Matt Williams 26 Jun '15

26 Jun '15

Dear All, I am trying to produce a Map, where the (tricky) idea is that the key is a pair, (t1, t2), and the key is considered identical under ordering. Thus: (t1, t2) is the same as (t2, t1) but (t1, t3) is not the same as (t1,t2). This LOOKS like a equality definition. However, the Map key typeclass is defined as Ord, which requires me to define compare: instance Ord Edge where (Edge s1 _) `compare` (Edge s2 _) = s1 `compare` s2 I am a bit stuck on how to use compare to define this type of eqlaity - any pointers very gratefully received. BW, Matt

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Functor fmap: how to
by Imants Cekusins 26 Jun '15

26 Jun '15

There are a few Functor & fmap tutorials. Here is basic use of fmap. If it leaves you confused, please ignore it. module FunctorFmap where {- why maybe & list? Functor instances exist for Maybe & List http://hackage.haskell.org/package/base-4.8.0.0/docs/Data-Functor.html#t:Fu… expand "instances" -} -- (a -> b) add3:: Int -> Int add3 = (+ 3) -- maybe runMaybe::IO () runMaybe = do print $ maybeFmap $ Just 1 print $ maybeInfixed $ Just 1 print $ maybeFmap Nothing print $ maybeInfixed Nothing -- maybeFmap & maybeInfixed do the same thing. different syntax maybeFmap::Maybe Int -> Maybe Int maybeFmap = fmap add3 maybeInfixed::Maybe Int -> Maybe Int maybeInfixed mi = add3 <$> mi -- list runList::IO () runList = do print $ listFmap [1,2] print $ listInfixed [1,2] -- listFmap & listInfixed do the same thing. different syntax listFmap::[Int] -> [Int] listFmap = fmap add3 listInfixed::[Int] -> [Int] listInfixed l = add3 <$> l

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basic use of Applicative
by Imants Cekusins 25 Jun '15

25 Jun '15

module BasicApplicative where -- 2 arg upd2:: Int -> Int -> Int upd2 x1 x2 = x1 * x2 -- 3 arg upd3:: Int -> Int -> Int -> Int upd3 x1 x2 x3 = x1 * x2 + x3 -- pure pureMaybe::Int -> Maybe Int pureMaybe = pure pureList::Int -> [Int] pureList = pure -- maybe maybe2::Maybe Int -> Maybe Int -> Maybe Int maybe2 mi1 mi2 = upd2 <$> mi1 <*> mi2 -- list list2::[Int] -> [Int] -> [Int] list2 l1 l2 = upd2 <$> l1 <*> l2 -- same result as list2 list2p::[Int] -> [Int] -> [Int] list2p l1 l2 = pure upd2 <*> l1 <*> l2 list3::[Int] -> [Int] -> [Int] -> [Int] list3 l1 l2 l3 = upd3 <$> l1 <*> l2 <*> l3

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