Tidy up tutorial

doc/tutorial/ApiType.lhs

@@ -328,14 +328,25 @@ type ProtectedAPI11
 
 ### Empty APIs
 
-TODO motivation...
+Sometimes it is useful to be able to generalise an API over the type of some
+part of it:
 
-``` haskell ignore
+``` haskell
-type UserAPI12
+type UserAPI12 innerAPI
-     = UserAPI
+     = UserAPI             -- this is the fixed bit of the API
- :<|> EmptyAPI -- this adds nothing to the API
+ :<|> "inner" :> innerAPI  -- this lets us put various other APIs under /inner
 ```
 
+If there is a case where you do not have anything extra to serve, you can use
+the `EmptyAPI` combinator to indicate this:
+
+``` haskell
+type UserAPI12Alone = UserAPI12 EmptyAPI
+```
+
+This also works well as a placeholder for unfinished parts of an API while it
+is under development.
+
 ### Interoperability with `wai`: `Raw`
 
 Finally, we also include a combinator named `Raw` that provides an escape hatch

doc/tutorial/Client.lhs

@@ -62,7 +62,6 @@ Enough chitchat, let's see an example. Consider the following API type from the
 type API = "position" :> Capture "x" Int :> Capture "y" Int :> Get '[JSON] Position
       :<|> "hello" :> QueryParam "name" String :> Get '[JSON] HelloMessage
       :<|> "marketing" :> ReqBody '[JSON] ClientInfo :> Post '[JSON] Email
-      :<|> EmptyAPI
 ```
 
 What we are going to get with **servant-client** here is three functions, one to query each endpoint:
@@ -89,11 +88,23 @@ the function `client`. It takes one argument:
 api :: Proxy API
 api = Proxy
 
-position :<|> hello :<|> marketing :<|> EmptyClient = client api
+position :<|> hello :<|> marketing = client api
 ```
 
 `client api` returns client functions for our _entire_ API, combined with `:<|>`, which we can pattern match on as above. You could say `client` "calculates" the correct type and number of client functions for the API type it is given (via a `Proxy`), as well as their implementations.
 
+If there is an `EmptyAPI` within your API, this matches the `EmptyClient`
+constructor:
+
+``` haskell ignore
+type API' = API :<|> EmptyAPI
+
+api' :: Proxy API'
+api' = Proxy
+
+(position' :<|> hello' :<|> marketing') :<|> EmptyClient = client api'
+```
+
 ``` haskell ignore
 -- | URI scheme to use
 data Scheme =

doc/tutorial/Docs.lhs

@@ -38,10 +38,9 @@ Like client function generation, documentation generation amounts to inspecting
 This time however, we have to assist **servant**. While it is able to deduce a lot of things about our API, it can't magically come up with descriptions of the various pieces of our APIs that are human-friendly and explain what's going on "at the business-logic level". A good example to study for documentation generation is our webservice with the `/position`, `/hello` and `/marketing` endpoints from earlier:
 
 ``` haskell
-type ExampleAPI = ("position" :> Capture "x" Int :> Capture "y" Int :> Get '[JSON] Position
+type ExampleAPI = "position" :> Capture "x" Int :> Capture "y" Int :> Get '[JSON] Position
       :<|> "hello" :> QueryParam "name" String :> Get '[JSON] HelloMessage
-      :<|> "marketing" :> ReqBody '[JSON] ClientInfo :> Post '[JSON] Email)
+      :<|> "marketing" :> ReqBody '[JSON] ClientInfo :> Post '[JSON] Email
-      :<|> EmptyAPI
 
 exampleAPI :: Proxy ExampleAPI
 exampleAPI = Proxy
@@ -221,7 +220,7 @@ api :: Proxy DocsAPI
 api = Proxy
 
 server :: Server DocsAPI
-server = (Server.server3 :<|> emptyServer) :<|> Tagged serveDocs where
+server = Server.server3 :<|> Tagged serveDocs where
     serveDocs _ respond =
         respond $ responseLBS ok200 [plain] docsBS
     plain = ("Content-Type", "text/plain")

doc/tutorial/Javascript.lhs

@@ -45,7 +45,6 @@ Now let's have the API type(s) and the accompanying datatypes.
 ``` haskell
 type API = "point" :> Get '[JSON] Point
       :<|> "books" :> QueryParam "q" Text :> Get '[JSON] (Search Book)
-      :<|> EmptyAPI
 
 type API' = API :<|> Raw
 
@@ -134,7 +133,6 @@ api' = Proxy
 server :: Server API
 server = randomPoint
     :<|> searchBook
-    :<|> emptyServer
 
 server' :: Server API'
 server' = server

doc/tutorial/Server.lhs

@@ -1020,10 +1020,11 @@ serverFor = error "..."
 -- or the mailing list if you get stuck!
 ```
 
-TODO prose
+If the API contains the `EmptyAPI` combinator, the corresponding server is
+called `emptyServer`:
 
 ``` haskell
-type CombinedAPI2 = API :<|> EmptyAPI
+type CombinedAPI2 = API :<|> "empty" :> EmptyAPI
 
 server11 :: Server CombinedAPI2
 server11 = server3 :<|> emptyServer