基本数据类型 #

-- Int类型
a :: Int
a = 42

-- Integer类型（可以很大）
b :: Integer
b = 123456789012345678901234567890

-- Word类型（无符号）
c :: Word
c = 100

-- Float（单精度）
piApprox :: Float
piApprox = 3.14159

-- Double（双精度，更常用）
precisePi :: Double
precisePi = 3.141592653589793

-- 科学计数法
bigNumber :: Double
bigNumber = 1.5e10    -- 15000000000.0
smallNumber :: Double
smallNumber = 1.5e-3  -- 0.0015

import Data.Ratio

-- 有理数
half :: Rational
half = 1 % 2

third :: Rational
third = 1 % 3

-- 精确计算
sumRational = half + third  -- 5 % 6

-- Num类方法
class Num a where
    (+) :: a -> a -> a
    (-) :: a -> a -> a
    (*) :: a -> a -> a
    negate :: a -> a
    abs :: a -> a
    signum :: a -> a
    fromInteger :: Integer -> a

-- 多态数值
x :: Num a => a
x = 42  -- 可以是Int、Integer、Double等

-- 布尔类型
flag :: Bool
flag = True

isFalse :: Bool
isFalse = False

-- 逻辑运算
andExample :: Bool
andExample = True && False  -- False

orExample :: Bool
orExample = True || False   -- True

notExample :: Bool
notExample = not True       -- False

-- 比较产生Bool
eq :: Bool
eq = 5 == 5   -- True

neq :: Bool
neq = 5 /= 3  -- True

lt :: Bool
lt = 3 < 5    -- True

gt :: Bool
gt = 5 > 3    -- True

-- if-then-else
absolute :: Int -> Int
absolute x = if x >= 0 then x else -x

-- 使用布尔函数
isEven :: Int -> Bool
isEven x = x `mod` 2 == 0

isOdd :: Int -> Bool
isOdd = not . isEven

-- Char类型
letter :: Char
letter = 'a'

digit :: Char
digit = '7'

symbol :: Char
symbol = '@'

newline :: Char
newline = '\n'

tab :: Char
tab = '\t'

backslash :: Char
backslash = '\\'

singleQuote :: Char
singleQuote = '\''

-- Unicode字符
chinese :: Char
chinese = '中'

-- Unicode码点
heart :: Char
heart = '\9829'  -- ♥

import Data.Char

-- 大小写转换
upper :: Char -> Char
upper = toUpper

lower :: Char -> Char
lower = toLower

-- 判断函数
isLetter :: Char -> Bool
isLetter = Data.Char.isLetter

isDigit :: Char -> Bool
isDigit = Data.Char.isDigit

isAlpha :: Char -> Bool
isAlpha = Data.Char.isAlpha

isSpace :: Char -> Bool
isSpace = Data.Char.isSpace

import Data.Char

-- 字符转数值
charToInt :: Char -> Int
charToInt c = ord c  -- 'A' -> 65

-- 数值转字符
intToChar :: Int -> Char
intToChar n = chr n  -- 65 -> 'A'

-- 数字字符转数值
digitToInt :: Char -> Int
digitToInt '5' = 5

-- 数值转数字字符
intToDigit :: Int -> Char
intToDigit 5 = '5'

type String = [Char]

-- 字符串字面量
greeting :: String
greeting = "Hello, World!"

-- 空字符串
empty :: String
empty = ""

-- 拼接
hello :: String
hello = "Hello" ++ " " ++ "World"

-- 反转
reversed :: String
reversed = reverse "hello"  -- "olleh"

-- 长度
len :: Int
len = length "hello"  -- 5

-- 取字符
first :: Char
first = head "hello"  -- 'h'

-- 取子串
take3 :: String
take3 = take 3 "hello"  -- "hel"

drop2 :: String
drop2 = drop 2 "hello"  -- "llo"

-- 数值转字符串
numToStr :: Int -> String
numToStr = show

-- 字符串转数值
strToNum :: String -> Int
strToNum = read

-- 安全转换
readMaybe :: Read a => String -> Maybe a
readMaybe s = case reads s of
    [(x, "")] -> Just x
    _         -> Nothing

-- 使用转义
multiLine :: String
multiLine = "Line 1\nLine 2\nLine 3"

-- 使用反引号（GHC扩展）
{-# LANGUAGE OverloadedStrings #-}
multiLine' :: String
multiLine' = unlines 
    [ "Line 1"
    , "Line 2"
    , "Line 3"
    ]

import qualified Data.Text as T
import qualified Data.ByteString as B
import qualified Data.ByteString.Char8 as BC

-- Text（Unicode字符串）
textStr :: T.Text
textStr = T.pack "Hello"

-- ByteString（二进制数据）
byteStr :: B.ByteString
byteStr = BC.pack "Hello"

-- Eq约束
isEqual :: Eq a => a -> a -> Bool
isEqual x y = x == y

-- Ord约束
maxOfThree :: Ord a => a -> a -> a -> a
maxOfThree x y z = max x (max y z)

-- Num约束
double :: Num a => a -> a
double x = x * 2

-- 多重约束
sumAndShow :: (Num a, Show a) => a -> a -> String
sumAndShow x y = show (x + y)

-- Num继承结构
class Num a where ...
class (Num a) => Fractional a where ...
class (Fractional a) => Floating a where ...

-- Ord继承Eq
class (Eq a) => Ord a where ...

-- 整数转换
intToInteger :: Int -> Integer
intToInteger = toInteger

integerToInt :: Integer -> Int
integerToInt = fromInteger

-- 浮点转换
intToDouble :: Int -> Double
intToDouble = fromIntegral

doubleToInt :: Double -> Int
doubleToInt = round  -- 或 floor, ceiling, truncate

-- 类型签名
fromIntegral :: (Integral a, Num b) => a -> b

-- 示例
intToFloat :: Int -> Float
intToFloat = fromIntegral

intToDouble :: Int -> Double
intToDouble = fromIntegral

-- 实际使用
average :: [Int] -> Double
average xs = fromIntegral (sum xs) / fromIntegral (length xs)

-- 类型签名
realToFrac :: (Real a, Fractional b) => a -> b

-- 示例
floatToDouble :: Float -> Double
floatToDouble = realToFrac

-- 编译器推断类型
add x y = x + y
-- 推断为：Num a => a -> a -> a

multiply x y = x * y
-- 推断为：Num a => a -> a -> a

isEqual x y = x == y
-- 推断为：Eq a => a -> a -> Bool

-- 默认规则
-- Num类型默认为Integer
-- Fractional类型默认为Double

number = 42      -- 默认为Integer
decimal = 3.14   -- 默认为Double