Documentation

RecordParam uses fields in a record to represent query parameters.

For each record field:

• The modified record field name becomes a query parameter name.
• The record field type becomes the query parameter type.

For example, this API:

type API = "users" :> (QueryParam "category" Category :>
                       QueryParam' '[Required, Strict] "sort_by" SortBy :>
                       QueryFlag "with_schema" :>
                       QueryParams "filters" Filter :>
                       Get '[JSON] User)

can be written using records:

data DropPrefixExp :: sym -> Exp sym

type instance Eval (DropPrefixExp sym) = DropPrefix sym

data UserParams = UserParams
  { _userParams_category :: Maybe Category
  , _userParams_sort_by :: SortBy
  , _userParams_with_schema :: Bool
  , _userParams_filters :: [Filter]
  }

type API = "users" :> RecordParam DropPrefixExp UserParams :> Get '[JSON] User

Here, DropPrefixExp wraps a sym into Exp.

The instance of Eval for DropPrefixExp sym drops the prefix of that sym via DropPrefix.

DropPrefix is applied to the fields of UserParams.

The "_userParams_category" record field corresponds to the query parameter "category".

Type family for rewriting a RecordParam API to a regular servant API. This family is useful for defining instances of classes that extract information from the API type, such as classes from servant-swagger or servant-foreign.

Typical use:

instance SomeClass (UnRecordParam (RecordParam mod a :> api))) =>
         SomeClass (RecordParam mod a :> api) where
   someMethod _ = someMethod (Proxy :: Proxy (UnRecordParam (RecordParam mod a :> api))