tutorial: make Client.lhs compile

This commit is contained in:
Sönke Hahn 2016-01-28 13:22:20 +01:00
parent 52b1a233fe
commit df363cecb0
2 changed files with 22 additions and 12 deletions

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@ -15,12 +15,14 @@ need to have some language extensions and imports:
module Client where
import Control.Monad.Trans.Either
import Control.Monad.Trans.Except
import Data.Aeson
import Data.Proxy
import GHC.Generics
import Network.HTTP.Client (Manager, newManager, defaultManagerSettings)
import Servant.API
import Servant.Client
import System.IO.Unsafe
```
Also, we need examples for some domain specific data types:
@ -70,13 +72,13 @@ What we are going to get with *servant-client* here is 3 functions, one to query
``` haskell
position :: Int -- ^ value for "x"
-> Int -- ^ value for "y"
-> EitherT ServantError IO Position
-> ExceptT ServantError IO Position
hello :: Maybe String -- ^ an optional value for "name"
-> EitherT ServantError IO HelloMessage
-> ExceptT ServantError IO HelloMessage
marketing :: ClientInfo -- ^ value for the request body
-> EitherT ServantError IO Email
-> ExceptT ServantError IO Email
```
Each function makes available as an argument any value that the response may depend on, as evidenced in the API type. How do we get these functions? Just give a `Proxy` to your API and a host to make the requests to:
@ -85,7 +87,12 @@ Each function makes available as an argument any value that the response may dep
api :: Proxy API
api = Proxy
position :<|> hello :<|> marketing = client api (BaseUrl Http "localhost" 8081)
{-# NOINLINE __manager #-}
__manager :: Manager
__manager = unsafePerformIO $ newManager defaultManagerSettings
position :<|> hello :<|> marketing =
client api (BaseUrl Http "localhost" 8081 "") __manager
```
As you can see in the code above, we just "pattern match our way" to these functions. If we try to derive less or more functions than there are endpoints in the API, we obviously get an error. The `BaseUrl` value there is just:
@ -109,21 +116,21 @@ data BaseUrl = BaseUrl
That's it. Let's now write some code that uses our client functions.
``` haskell
queries :: EitherT ServantError IO (Position, HelloMessage, Email)
queries :: ExceptT ServantError IO (Position, HelloMessage, Email)
queries = do
pos <- position 10 10
msg <- hello (Just "servant")
message <- hello (Just "servant")
em <- marketing (ClientInfo "Alp" "alp@foo.com" 26 ["haskell", "mathematics"])
return (pos, msg, em)
return (pos, message, em)
run :: IO ()
run = do
res <- runEitherT queries
res <- runExceptT queries
case res of
Left err -> putStrLn $ "Error: " ++ show err
Right (pos, msg, em) -> do
Right (pos, message, em) -> do
print pos
print msg
print message
print em
```

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@ -15,7 +15,7 @@ cabal-version: >=1.10
library
exposed-modules: ApiType
-- , Client
, Client
-- , Docs
-- , Javascript
-- , Server
@ -45,6 +45,9 @@ library
, http-types
, transformers
, markdown-unlit >= 0.4
, http-client
-- hs-source-dirs:
default-language: Haskell2010
ghc-options: -Wall -Werror -pgmL markdown-unlit
-- to silence aeson-0.10 warnings:
ghc-options: -fno-warn-missing-methods