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akhesaCaro 2022-02-24 12:08:57 +01:00
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doc/cookbook/namedRoutes/NamedRoutes.lhs
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@ -20,87 +20,6 @@ However, it should be understood that this cookbook does _not_ dwell on the
built-in servant combinators as the [Structuring APIs built-in servant combinators as the [Structuring APIs
](<../structuring-apis/StructuringApis.html>) cookbook already covers that angle. ](<../structuring-apis/StructuringApis.html>) cookbook already covers that angle.
## Why would I want to use `NamedRoutes` over the alternative `:<|>` operator?
With `NamedRoutes`, we don’t need to care about the declaration order of the endpoints.
For example, with the `:<|>` operator there’s room for error when the order of the API type
```haskell,ignore
type API1 = "version" :> Get '[JSON] Version
:<|> "movies" :> Get '[JSON] [Movie]
```
does not follow the `Handler` implementation order
```haskell,ignore
apiHandler :: ServerT API1 Handler
apiHandler = getMovies
:<|> getVersion
```
GHC could scold you with a very tedious message such as :
```console
• Couldn't match type 'Handler NoContent'
with 'Movie -> Handler NoContent'
Expected type: ServerT MovieCatalogAPI Handler
Actual type: Handler Version
:<|> ((Maybe SortBy -> Handler [Movie])
:<|> ((MovieId -> Handler (Maybe Movie))
:<|> ((MovieId -> Movie -> Handler NoContent)
:<|> (MovieId -> Handler NoContent))))
• In the expression:
versionHandler
:<|>
movieListHandler
:<|>
getMovieHandler :<|> updateMovieHandler :<|> deleteMovieHandler
In an equation for 'server':
server
= versionHandler
:<|>
movieListHandler
:<|>
getMovieHandler :<|> updateMovieHandler :<|> deleteMovieHandler
|
226 | server = versionHandler
```
On the contrary, with the `NamedRoutes` technique, we refer to the routes by their name:
```haskell,ignore
data API mode = API
{ list :: "list" :> ...
, delete :: "delete" :> ...
}
```
and GHC follows the lead :
```console
• Couldn't match type 'NoContent' with 'Movie'
Expected type: AsServerT Handler :- Delete '[JSON] Movie
Actual type: Handler NoContent
• In the 'delete' field of a record
In the expression:
MovieAPI
{get = getMovieHandler movieId,
update = updateMovieHandler movieId,
delete = deleteMovieHandler movieId}
In an equation for 'movieHandler':
movieHandler movieId
= MovieAPI
{get = getMovieHandler movieId,
update = updateMovieHandler movieId,
delete = deleteMovieHandler movieId}
|
252 | , delete = deleteMovieHandler movieId
```
So, NamedRoutes is more readable for a human, and GHC gives you more accurate error messages.
What are we waiting for?
## Boilerplate time! ## Boilerplate time!