Question

以下代码会产生此错误：

module Broken1 where

import Control.Monad.Aff.Class (MonadAff)
import Control.Monad.Aff (Aff())
import DOM.HTML.Types
import Halogen
import DOM
import Control.Monad.Eff.Exception
import Control.Monad.Aff.AVar
import Prelude

import qualified Halogen.HTML.Indexed as H

data State = State
data Query a = Query a

ui :: forall eff g. (MonadAff (HalogenEffects eff) g) => Component State Query g
ui = component (\_ -> H.div_ []) (\(Query next) -> pure next)

main' :: forall eff a. (HTMLElement -> Aff (HalogenEffects eff) a) 
                 -> Aff (HalogenEffects eff) Unit
main' addToDOM = do
    { node: node, driver: driver } <- runUI ui State

    let driver' :: Natural Query (Aff (HalogenEffects eff))
        driver' = driver

    return unit

错误：

  at Broken1.purs line 34, column 19 - line 36, column 5

    Could not match type
      a2
    with type
      a1

  while trying to match type a2
    with type a1
  while checking that expression driver
    has type Query a1 -> Aff ( avar :: AVAR
                             , err :: EXCEPTION
                             , dom :: DOM
                             | eff1
                             )
                         a1
  in value declaration main'

如果省略driver'的类型签名，则没有编译器错误，正如我所希望的那样。如果我问psc签名（通过用_替换类型），这是建议：

Wildcard type definition has the inferred type

forall a. Query a -> Aff ( dom :: DOM
                         , err :: EXCEPTION
                         , avar :: AVAR
                         | eff4
                         )
                     a

当我将其剪切并粘贴到代码中而不是原始类型时，错误与上面相同。

在第二种情况下，这实际上是有道理的，因为量词打开了一个新的范围，应该在主要的签名中捕获。但即使我删除forall a，类型错误仍然存在。

garyb今天早些时候在#purescript上说它可能是类型检查器中的一个错误。无论如何我都会在这里张贴这个，直到确定事实为止。

谢谢！（：

purescript类型签名无法编译，代码工作正常没有;建议签名不起作用

0 个答案: