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We define `ServerT (NamedRoutes api) m` as `api (AsServerT m)`, so that the server of an record-defined API is a record of handlers. The implementation piggy backs on the instance for “vanilla” servant types with `(:<|>)`, using the `GServantProduct` for converting backd and forth between the record / vanilla servers. The main difficulty is that GHC needs to know that this operation is legit, which can be expressed as the fact that: ``` GToServant (Rep (ServerT (NamedRoutes api))) m ~ ServerT (GToServant (Rep (api AsApi))) m ``` plus a few additional constraints. This is easy enough for `route`, as we know that `m ~ Handler`. But in the case of `hoistServerWithContext`, the two involved monads are unknown ; in other words, this constraint needs to hold `forall m.` Switching `-XQuantifiedConstraints` on is not sufficient, as our constraints involve type families (`Rep` and `ServerT`). Our trick is to use an intermediary typeclass, `GServer`, as a provider of evidence (in the form of a `Dict`) that our constraints are indeed satisfied for a particular monad. The only instance of `GServer` is defined along with it, so it is practically invisible to users. |
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| example | ||
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| test | ||
| CHANGELOG.md | ||
| LICENSE | ||
| README.md | ||
| servant-server.cabal | ||
| Setup.hs | ||
servant-server
This library lets you implement an HTTP server with handlers for each endpoint of a servant API, handling most of the boilerplate for you.
Getting started
We've written a tutorial guide that introduces the core types and features of servant. After this article, you should be able to write your first servant webservices, learning the rest from the haddocks' examples.