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Merge pull request #626 from haskell-servant/jkarni/response-header-tutorial

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Add more documentation about response headers to tutorial.
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Julian Arni 2016-10-26 16:28:54 +01:00 committed by GitHub
commit cd9bc8b52f
1 changed files with 23 additions and 1 deletions
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24
doc/tutorial/Server.lhs
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@ -753,7 +753,29 @@ myHandler :: Server MyHandler
myHandler = return $ addHeader 1797 albert myHandler = return $ addHeader 1797 albert
``` ```
Note that the type of `addHeader x` is different than the type of `x`! Note that the type of `addHeader header x` is different than the type of `x`!
And if you add more headers, more headers will appear in the header list:
``` haskell
type MyHeadfulHandler = Get '[JSON] (Headers '[Header "X-A-Bool" Bool, Header "X-An-Int" Int] User)
myHeadfulHandler :: Server MyHeadfulHandler
myHeadfulHandler = return $ addHeader True $ addHeader 1797 albert
```
But what if your handler only *sometimes* adds a header? If you declare that
your handler adds headers, and you don't add one, the return type of your
handler will be different than expected. To solve this, you have to explicitly
*not* add a header by using `noHeader`:
``` haskell
type MyMaybeHeaderHandler
= Capture "withHeader" Bool :> Get '[JSON] (Headers '[Header "X-An-Int" Int] User)
myMaybeHeaderHandler :: Server MyMaybeHeaderHandler
myMaybeHeaderHandler x = return $ if x then addHeader 1797 albert
else noHeader albert
```
## Serving static files ## Serving static files