add an example on how to derive client functions for Hackage

servant-examples/LICENSE

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+Copyright (c) 2015, Alp Mestanogullari
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of Alp Mestanogullari nor the names of other
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

servant-examples/Setup.hs

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+import Distribution.Simple
+main = defaultMain

servant-examples/hackage/hackage.hs

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+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE OverloadedStrings #-}
+import Control.Applicative
+import Control.Monad
+import Control.Monad.IO.Class
+import Control.Monad.Trans.Either
+import Data.Aeson
+import Data.Monoid
+import Data.Proxy
+import Data.Text (Text)
+import GHC.Generics
+import Servant.API
+import Servant.Client
+
+import qualified Data.Text    as T
+import qualified Data.Text.IO as T
+
+type HackageAPI =
+	     "users" :> Get '[JSON] [UserSummary]
+  :<|> "user" :> Capture "username" Username :> Get '[JSON] UserDetailed
+  :<|> "packages" :> Get '[JSON] [Package]
+
+type Username = Text
+
+data UserSummary = UserSummary
+  { summaryUsername :: Username
+  , summaryUserid   :: Int
+  } deriving (Eq, Show)
+
+instance FromJSON UserSummary where
+  parseJSON (Object o) =
+    UserSummary <$> o .: "username"
+                <*> o .: "userid"
+
+  parseJSON _ = mzero
+
+type Group = Text
+
+data UserDetailed = UserDetailed
+  { username :: Username
+  , userid   :: Int
+  , groups   :: [Group]
+  } deriving (Eq, Show, Generic)
+
+instance FromJSON UserDetailed
+
+newtype Package = Package { packageName :: Text }
+  deriving (Eq, Show, Generic)
+
+instance FromJSON Package
+
+hackageAPI :: Proxy HackageAPI
+hackageAPI = Proxy
+
+getUsers :: BaseUrl -> EitherT ServantError IO [UserSummary] 
+getUser :: Username -> BaseUrl -> EitherT ServantError IO UserDetailed
+getPackages :: BaseUrl -> EitherT ServantError IO [Package]
+getUsers :<|> getUser :<|> getPackages = client hackageAPI
+
+run :: (BaseUrl -> r) -> r
+run f = f (BaseUrl Http "hackage.haskell.org" 80)
+
+main :: IO ()
+main = print =<< uselessNumbers
+
+uselessNumbers :: IO (Either ServantError ())
+uselessNumbers = runEitherT $ do
+  users <- run getUsers
+  liftIO . putStrLn $ show (length users) ++ " users"
+
+  user <- liftIO $ do
+    putStrLn "Enter a valid hackage username"
+    T.getLine
+  userDetailed <- run (getUser user)
+  liftIO . T.putStrLn $ user <> " maintains " <> T.pack (show (length $ groups userDetailed)) <> " packages"
+  
+  packages <- run getPackages 
+  let monadPackages = filter (isMonadPackage . packageName) packages
+  liftIO . putStrLn $ show (length monadPackages) ++ " monad packages"
+
+  where isMonadPackage = T.isInfixOf "monad"

servant-examples/servant-examples.cabal

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+name:                servant-examples
+version:             0.3
+synopsis:            Example programs for servant
+description:         Example programs for servant
+homepage:            http://haskell-servant.github.io/
+license:             BSD3
+license-file:        LICENSE
+author:              Alp Mestanogullari
+maintainer:          alpmestan@gmail.com
+-- copyright:           
+category:            Web
+build-type:          Simple
+-- extra-source-files:  
+cabal-version:       >=1.10
+
+executable hackage
+  main-is:             hackage.hs
+  -- other-modules:       
+  -- other-extensions:
+  build-depends:
+      aeson >= 0.8
+    , base >=4.7
+    , either
+    , servant
+    , servant-client
+    , text
+    , transformers
+  hs-source-dirs:      hackage
+  default-language:    Haskell2010