＜Practical Web Development with Haskell Master the Essential＞勘误

- 日理万妓 2022-11-05 13:57 17阅读 0赞

本文档为《Practical Web Development with Haskell Master the Essential Skills to Build Fast and Scalable Web Applications》勘误文档

操作系统  mac 10.15.7

1.安装stack\[P19\]

我采用curl方式进行安装

2.IDE \[P21\]

书中采用Haskero。但是经过blog确认，此插件已经不在维护，我安装VsCode和Haskell(legacy).所以跳过\`stack build intero\`

这里因为要安装旧版本的ghc，需要在stack.yaml中，更新下resolver为\`lts-14.21\`,并且屏蔽掉其他已经打开的resolver,这样才能下载8.4.2  8.6.5的ghc，否则默认会下载8.10版本，后续的package安装会有点问题。

2.1 getZonedTime\[P37\]

getZonedTime存在于多个time相关package中，按照上面的添加了time-lens后，需要在repl中先引入包 import Data.Time.Lens

然后才能使用zt <- getZonedTime

3.Regular Expression\[P38\]

3.1 首先安装pcre,这里没有采用brew进行安装，直接使用裸装。步骤如下

http://www.pcre.org
    curl --rempote-name https://ftp.pcre.org/pub/pcre/pcre-8.44.tar.gz
    tar -xzvf pcre-8.44.tar.gz
    ./configure --prefix=/Users/brant/program/libs/pcre-8.44-bin
    make
    make install
    sudo ln -s /Users/brant/program/libs/pcre-8.44-bin /usr/local/pcre
    echo 'export PATH=/usr/local/pcre/bin:$PATH' >> ~/.bash_profile
    source ~/.bash_profile
    pcre-config --version

3.2 安装pkg-config，步骤如下（这里注意需要安装0.29.2版本。如果安装0.29版本则会在高版本的mac上出现编译错误）

curl --remote-name https://pkgconfig.freedesktop.org/releases/pkg-config-0.29.2.tar.gz
    tar -zxvf pkg-config-0.29.2.tar.gz
    LDFLAGS="-framework CoreFoundation -framework Carbon"
    ./configure --with-internal-glib
    make 
    sudo make install

3.3这里安装完毕后，按道理应该可以自动引入pcre.h，但是在我的环境中是找不到的，所以我采用了一个折衷的办法

编译
    stack. build --extra-iunclude-dirs=/usr/local/pcre/include
    
    执行repl
    stack repl --extra-iunclude-dirs=/usr/local/pcre/include

如此便可以正确执行书中的regual相关代码

4.Json\[44\]

需要注意，因为我们上面已经新建了项目和main.hs，所以大部分同学应该在这里已经切换到非repl中执行了。

书中的代码‘$(deriveJSON defaultOptions "User)’ 在.hs文件中要修改为

instance ToJSON User where
         toJSON (User uId name hobbies) = object [ "id" .= uId , "name" .= name,"hobbies" .= hobbies ]
     instance FromJSON User where
        parseJSON = withObject "User" $ \v -> User <$> v .: "id" <*> v .: "name" <*> v .: "hobbies"
    
    -- 上面和下面等价。注意没有$()
    
     deriveJSON defaultOptions ''User

4.Exception\[P48\]

书中说因为ClassyPrelude自动引入了safe-exceptions.所以就自动获得了throw.但是我实际执行下来是没有自动引入的。如果非手动导入会获得如下错误

<interactive>:1:7: error:
        Variable not in scope: throw :: MyException -> IO ()

解决办法肯定是自己手动导入

import Control.Exception.Safe (throw)

至此，相关代码如下

package.yaml
    
    dependencies:
    - base >= 4.7 && < 5
    - classy-prelude
    - time
    - time-lens
    - pcre-heavy
    - aeson
    - template-haskell
    - text
    - safe-exceptions
    
    default-extensions:
    - NoImplicitPrelude
    - OverloadedStrings
    - QuasiQuotes
    - TemplateHaskell
    - DeriveGeneric
    - DeriveAnyClass
    
    stack.yaml
    
    # resolver: lts-3.5
    # resolver: nightly-2015-09-21
    # resolver: ghc-7.10.2
    resolver: lts-14.21
    
    
    Main.hs
    
    module Main where
    
    
    import ClassyPrelude
    import Lib
    import GHC.Generics
    import Data.Aeson
    import Language.Haskell.TH.Syntax (nameBase)  
    import Data.Aeson.TH
    import Data.Aeson.TH (deriveJSON, defaultOptions)
    import Control.Exception.Safe (throw)
    
    
    data User = User{ userId :: Int, userName :: Text, userHobbies :: [Text] } deriving (Show, Generic)
    
    -- instance ToJSON User where
    --     toJSON (User uId name hobbies) = object [ "id" .= uId , "name" .= name,"hobbies" .= hobbies ]
    -- instance FromJSON User where
    --    parseJSON = withObject "User" $ \v -> User <$> v .: "id" <*> v .: "name" <*> v .: "hobbies"
    -- deriveJSON defaultOptions ''User
    
    let structName = nameBase ''User
        lowercaseFirst (x:xs) = toLower [x] <> xs 
        lowercaseFirst xs = xs
        options = defaultOptions{ fieldLabelModifier = lowercaseFirst . drop (length structName)
        }
        in deriveJSON options ''User
    
    --- 如果想要替换生成的key格式，可以使用 camelTo2 替换 lowercaseFirst
    -- camelTo2 :: Char -> String -> String
    -- Here’s a usage example:
    -- camelTo2 '_' 'CamelAPICase' == "camel_api_case" 
    -- camelTo2 '-' 'userHobbies' == "user-hobbies"
    
    
    -- isBelow10 :: Int -> Bool
    -- isBelow10 n = if n < 10 then True else (error "above 10!")
    
    isBelow10E :: Int -> Either Text ()
    isBelow10E  n  = if n < 10 then Right() else Left (error "above 10!")
    
    
    run :: Int ->  IO ()
    run n = case isBelow10E n  of 
                Left e -> do
                    putStrLn "some went wrong!"
                    putStrLn e
                Right _ ->
                    putStrLn "All good!"
    
    main :: IO ()
    main = someFunc 
    
    
    data ServerException = ServerOnFireException | ServerNotPluggedInException deriving(Show)
    instance Exception ServerException
    data MyException = ThisException | ThatException deriving(Show)
    instance Exception MyException 
    
    run1 :: IO () -> IO ()
    run1 action = action
                `catch` (\e -> putStrLn $  tshow (e::ServerException) )
                `catch` (\e -> putStrLn $  tshow (e::MyException))
                `catchAny` (\e -> putStrLn $ tshow e)