Documentation

Type class that represents f denotes the type of field names of InterfaceOf f

f :|: g is the disjoint union of label f and label g. Use this type when you want to specify a protocol for multiple interfaces.

Example

data FooService = FooService {
  foo :: Int -> IO Bool,
  ...
  }
data BarService = BarService {
  bar :: String -> IO (),
  ...
  }
deriveLabel ''FooService
deriveLabel ''BarService

proto :: ProtocolM (FooServiceLabel :|: BarServiceLabel) ()
proto = do
  i1 <- decl $ whenArgs (L Foo) (==1) `thenReturn` True
  void $ decl $ whenArgs (R Bar) (=="bar") `thenReturn` () `dependsOn` [i1]

main :: IO ()
main = withProtocol proto $ \(fooService, barService) -> do
  ...

Generate the label type from given interface type.

• Define GADT XXXLabel m for interface XXX.

  • FieldX :: XXXLabel X for each field fieldX :: X where X is a standard type.

  • PolyFieldX :: XXXLabel ty[Dynamic/a] for each field of the form polyFieldX :: (forall a. Typeable a => ty)

    • Type variable a is substituted with DynamicShow if a is instances of Show and Typeable
    • Type variable a is substituted with Dynamic if a is an instance of Typeable but not Show
    • Report an error if type variable a is not an instance of Typeable
• Define instance Label XXXLabel.

Example

data API env = API {
    _foo :: Int -> RIO env Int,
    _bar :: forall a. (Show a, Typeable a) => String -> RIO env (Maybe a),
    _baz :: forall b. (Typeable a) => b -> RIO env ()
  }

deriveLabel ''API will generate the following code.

data APILabel env m where
    Foo :: APILabel env (Int -> RIO env Int)
    Bar :: APILabel env (String -> RIO env (Maybe DynamicShow)) -- type variable `a` is replaced with DynamicShow
    Baz :: APILabel env (Dynamic -> RIO env ()) -- type variable 'b' is replaced with Dynamic

instance Label (APILabel env) where
    type InterfaceOf (APILabel env) = API env
    toInterface k = API (k Foo) (castMethod (k Bar)) (castMethod (k Baz))
    showLabel x = case x of
      Foo -> Foo
      Bar -> Bar
      Baz -> Baz