Question

我想做一些非常简单的事情;发出wreq响应并将内容打印到终端。

main.hs看起来像这样： { - #LANGUAGE OverloadedStrings＃ - }

module Main where

import Network.Wreq
import qualified Data.ByteString.Char8 as C

main :: IO ()
main = do
  r <- get "http://httpbin.org/get"
  putStrLn (C.unpack r)

为什么呢？因为r似乎是一个字节串，所以它应该是无法打包的。

Prelude> import Network.Wreq
Prelude Network.Wreq> r <- get "http://httpbin.org/get"
Prelude Network.Wreq> :type r
r :: Response Data.ByteString.Lazy.Internal.ByteString

我的.cabal文件如下所示：

executable wreqscraper
  hs-source-dirs:      src
  main-is:             Main.hs
  default-language:    Haskell2010
  build-depends:       base >= 4.7 && < 5,
                       wreq,
                       bytestring

当我尝试用stack build构建它时，我得到了这个：

/Users/mkaravan/end2end/haskell_sandbox/wreqscraper/src/Main.hs:22:22: error:
    • Couldn't match expected type ‘C.ByteString’
                  with actual type ‘Response
                                      Data.ByteString.Lazy.Internal.ByteString’
    • In the first argument of ‘C.unpack’, namely ‘r’
      In the first argument of ‘putStrLn’, namely ‘(C.unpack r)’
      In a stmt of a 'do' block: putStrLn (C.unpack r)

使用putStrLn（或类似内容）打印这些内容的正确方法是什么？

Answer 1

您需要打开Response ByteString，以便获得ByteString，然后将其与C.unpack一起使用。

这是一个有效的例子：

{-# LANGUAGE OverloadedStrings #-}

import Network.Wreq
import Control.Lens
import Data.ByteString.Lazy.Char8 as C

main :: IO ()
main = do
    r <- get "http://httpbin.org/get"
    Prelude.putStrLn $ C.unpack $ (r ^. responseBody)

打印到终端的wreq响应

1 个答案: