最佳实践 #

-- 标准模块结构
module MyLib.ModuleName (
    -- 类型导出
    Type(..),
    
    -- 函数导出
    function1,
    function2,
    
    -- 重导出
    module Data.Maybe
) where

import Data.Maybe

-- 类型定义
data Type = ...

-- 函数定义
function1 = ...

module MyModule where

-- 标准库
import Data.List (sort, nub)
import Data.Maybe (fromMaybe)
import Control.Monad (forM_, when)

-- 第三方库
import qualified Data.Text as T
import qualified Data.Map as M

-- 本地模块
import MyLib.Types
import MyLib.Utils

my-project/
├── app/              # 可执行文件
│   └── Main.hs
├── src/              # 库代码
│   └── MyLib/
│       ├── Types.hs
│       ├── Core.hs
│       └── Utils.hs
├── test/             # 测试
│   └── MyLib/
│       └── CoreSpec.hs
├── benchmark/        # 性能测试
│   └── Bench.hs
├── README.md
├── ChangeLog.md
├── LICENSE
├── package.yaml
└── stack.yaml

-- 始终添加类型签名
function :: Int -> String -> Bool
function n s = n > length s

-- 类型类约束放在签名中
process :: (Show a, Eq a) => a -> String
process x = show x

-- 简单函数：单行
add :: Int -> Int -> Int
add x y = x + y

-- 复杂函数：使用where或let
complexCalc :: Int -> Int
complexCalc x = result
  where
    step1 = x * 2
    step2 = step1 + 1
    result = step2 ^ 2

-- 使用模式匹配而非if-then-else
describe :: Int -> String
describe 0 = "zero"
describe 1 = "one"
describe n
    | n < 0     = "negative"
    | otherwise = "many"

-- 使用模式匹配解构
process :: (Int, String) -> String
process (n, s) = s ++ ": " ++ show n

-- 使用newtype区分类型
newtype UserId = UserId Int
newtype ProductId = ProductId Int

-- 而非
-- type UserId = Int
-- type ProductId = Int

import Data.List (foldl')

-- 使用foldl'而非foldl
sum' :: [Int] -> Int
sum' = foldl' (+) 0

-- 使用严格数据类型
data Config = Config
    { configHost :: !String
    , configPort :: !Int
    }

-- 不好：构建大量thunk
badSum :: [Int] -> Int
badSum [] = 0
badSum (x:xs) = x + badSum xs

-- 好：使用严格累加器
goodSum :: [Int] -> Int
goodSum = go 0
  where
    go !acc [] = acc
    go !acc (x:xs) = go (acc + x) xs

import qualified Data.Map as M
import qualified Data.Set as S
import qualified Data.Vector as V

-- 频繁查找：使用Map
lookupTable :: M.Map String Int

-- 唯一元素：使用Set
uniqueItems :: S.Set Int

-- 随机访问：使用Vector
randomAccess :: V.Vector Double

-- 使用INLINE编译指示
{-# INLINE criticalFunction #-}
criticalFunction :: Int -> Int
criticalFunction = (*2)

-- 使用Maybe处理可能失败的操作
safeHead :: [a] -> Maybe a
safeHead [] = Nothing
safeHead (x:_) = Just x

-- 使用Either提供错误信息
safeDiv :: Int -> Int -> Either String Int
safeDiv _ 0 = Left "Division by zero"
safeDiv x y = Right (x `div` y)

-- 不好：部分函数可能崩溃
head :: [a] -> a
tail :: [a] -> [a]

-- 好：使用安全版本
safeHead :: [a] -> Maybe a
safeTail :: [a] -> Maybe [a]

data AppError
    = NetworkError String
    | ParseError String
    | ValidationError String
    deriving (Show)

handleError :: AppError -> IO ()
handleError (NetworkError msg) = putStrLn $ "Network: " ++ msg
handleError (ParseError msg) = putStrLn $ "Parse: " ++ msg
handleError (ValidationError msg) = putStrLn $ "Validation: " ++ msg

-- test/MyLib/CoreSpec.hs
module MyLib.CoreSpec (spec) where

import Test.Hspec
import MyLib.Core

spec :: Spec
spec = do
    describe "add" $ do
        it "adds two numbers" $ do
            add 1 2 `shouldBe` 3
        
        it "handles zero" $ do
            add 0 0 `shouldBe` 0

import Test.QuickCheck

prop_addCommutative :: Int -> Int -> Bool
prop_addCommutative x y = add x y == add y x

prop_addIdentity :: Int -> Bool
prop_addIdentity x = add x 0 == x

# 使用HSpec
cabal test

# 使用QuickCheck
quickCheck prop_addCommutative

import Debug.Trace

-- 添加调试输出
debugFunction :: Int -> Int
debugFunction x = trace ("input: " ++ show x) (x * 2)

-- 带标签的调试
debugFunction' :: Int -> Int
debugFunction' x = traceShowId x * 2

-- 在GHCi中
:break function  -- 设置断点
:step            -- 单步执行
:continue        -- 继续
:print var       -- 打印变量

-- 使用TypedHoles
function :: Int -> String
function x = _  -- 编译器会提示类型

-- 使用TypeApplications
show @Int 42  -- 显式指定类型

-- | 计算两个数的和
--
-- >>> add 1 2
-- 3
add :: Int -> Int -> Int
add x y = x + y

-- | 安全除法
--
-- 返回 'Nothing' 如果除数为零
safeDiv :: Int -> Int -> Maybe Int
safeDiv _ 0 = Nothing
safeDiv x y = Just (x `div` y)

-- |
-- Module      : MyLib.Core
-- Description : 核心功能
-- Copyright   : (c) Author, 2024
-- License     : BSD-3-Clause
--
-- 核心功能模块
module MyLib.Core (
    -- * 基本操作
    add,
    subtract,
    
    -- * 高级操作
    multiply,
    divide
) where

# 使用ormolu
ormolu --mode inplace src/**/*.hs

# 使用fourmolu
fourmolu --mode inplace src/**/*.hs

# 使用hlint
hlint src/

# 使用weeder
weeder .

# 编译时启用分析
cabal build --enable-profiling

# 运行分析
cabal run my-project +RTS -p