Haskell Purescript，了解为什么找不到类型类实例
我正在尝试构建一个简单的Purescript应用程序，但我不明白为什么我总是遇到typeclass实例错误 具体地说，在我的Haskell Purescript，了解为什么找不到类型类实例,haskell,purescript,Haskell,Purescript,我正在尝试构建一个简单的Purescript应用程序，但我不明白为什么我总是遇到typeclass实例错误 具体地说，在我的组件中我定义了eval函数来操作我的查询代数。在这个过程中，我只是为了好玩而把一些东西记录到控制台上 type AppEffects eff = (HalogenEffects (console :: CONSOLE | eff)) data Query a = DoSomething a eval :: Query ~> H.ComponentDSL State
组件中evaltype AppEffects eff = (HalogenEffects (console :: CONSOLE | eff))
data Query a = DoSomething a
eval :: Query ~> H.ComponentDSL State Query (Aff (AppEffects eff))
eval (DoSomething a) = do
liftEff $ log "print me out!"
-- do some stuff with the action
pure next
No type class instance was found for
Control.Monad.Eff.Class.MonadEff ( "console" :: CONSOLE
| t0
)
(Free
(HalogenFP EventSource
{ "someState" :: String
}
Query
(Aff
( "avar" :: AVAR
, "err" :: EXCEPTION
, "dom" :: DOM
, "console" :: CONSOLE
| eff1
)
)
)
)
The instance head contains unknown type variables. Consider adding a type annotation.
tryPrint :: Eff (console :: CONSOLE | eff) Unit
tryPrint = log "print me out!"
但是，编译器仍然告诉我需要为
MonadEffFreeMonadEffComponentDSLliftEffFree这在下一个卤素版本中发生了变化，
ComponentDSLMonadEfffromEffFreeMonadEff组件DSLliftEffFreeComponentDSLMonadEfffromEff