Question

以下功能没有进行类型检查：

import qualified Control.Exception as E
import Data.Conduit (ResourceT)
import Network.HTTP.Types (Method, Status(..))
import Network.HTTP.Conduit
import qualified Data.ByteString.Lazy.Char8 as LBS

doHttps :: Method -> String
        -> Maybe (RequestBody (ResourceT IO))
        -> IO (Either E.SomeException (Response LBS.ByteString))
doHttps reqMethod url body = undefined

它会产生以下错误：

RequestBody is applied to too many type arguments
    In the type signature for `doHttps':
      doHttps :: Method
                 -> String
                    -> Maybe (RequestBody (ResourceT IO))
                       -> IO (Either E.SomeException (Response LBS.ByteString))
Failed, modules loaded: none.

doHttps函数是this function的简化版本。但显然模块中的原始功能是typechecks，但上面的代码片段不起作用。为什么会这样？

Answer 1

不同版本的http-conduit库。在版本1. *中，RequestBody采用了类型参数：

http://hackage.haskell.org/package/http-conduit-1.9.6/docs/Network-HTTP-Conduit.html#t:RequestBody

但是，在版本2. *中，它不带类型参数：

http://hackage.haskell.org/package/http-conduit-2.0.0/docs/Network-HTTP-Conduit.html#t:RequestBody

RequestBody应用于太多类型参数

1 个答案: