zwvista的专栏

Arrowclass Category a => Arrow a where arr :: (b -> c) -> a b c first :: a b c -> a (b,d) (c,d) first = (*** id) second :: a b c -> a (d,b) (d,c) second = (id ***) (***) :: a b c -

Comonadclass Functor w => Comonad w where extract :: w a -> a duplicate :: w a -> w (w a) duplicate = extend id extend :: (w a -> b) -> w a -> w b extend f = fmap f . duplicateComonad 是个类型类。比较

Text.Regex.PCRE.Heavy$ brew install pcre$ cabal install pcre-heavyInstalled pcre-heavy-1.0.0.2Prelude> :m +Text.Regex.PCRE.HeavyPrelude Text.Regex.PCRE.Heavy> Prelude Text.Regex.PCRE.Heavy> :set -X

Data.SequenceConstructionPrelude Data.Sequence> emptyfromList []Prelude Data.Sequence> singleton 3fromList [3]Prelude Data.Sequence> 3 <| fromList [4,5]fromList [3,4,5]Prelude Data.Sequence> from

Data.SetConstructionPrelude> import Data.Set as SPrelude S> emptyfromList []Prelude S> singleton 5fromList [5]Prelude S> insert 3 $ fromList [4,5]fromList [3,4,5]Prelude S> delete 5 $ fromList [

Semigroupclass Semigroup a where (&lt;&gt;) :: a -&gt; a -&gt; a sconcat :: NonEmpty a -&gt; a stimes :: Integral b =&gt; b -&gt; a -&gt; aclass Semigroup a =&gt; Monoid ...

安装 free 包$ cabal install freeInstalled free-5.0.2Free Monaddata Free f a = Pure a | Free (f (Free f a))instance Functor f =&gt; Functor (Free f) where fmap f = go where go (Pure a...

Existentials（存在类型）Existentially quantified types（Existentially types，Existentials）是一种将一组类型归为一个类型的方式。 通常在使用 type, newtype, data 定义新类型的时候，出现在右边的类型参数必须出现在左边。 存在类型可以突破此限制。实例{-# LANGUAGE Existe...

GADTsGADTs（Generalised Algebraic Data Types，广义代数数据类型）是对代数数据类型的一种扩展。 它允许在定义数据类型时明确指定类型参数的类型并使用模式匹配。--ADTdata Maybe a = Nothing | Just a--GADTdata Maybe a where Nothing :: May...

Extra安装 extra 模块。$ cabal install extraInstalled extra-1.6Prelude> :m +ExtraPrelude Extra> Data.List.Extra String operationsPrelude Extra> lower "This is A TEST""this is a test"Prelude Extra> upper

Data.ByteStringString 是 [Char] 的同义词，在使用上存在List的惰性所带来的性能问题。 在处理大型二进制文件时，可以使用 ByteString 来代替 String。 ByteString 类型分为以下两种： * Lazy 模块 Data.ByteString.Lazy 中的 Data.ByteString.Lazy.ByteString Lazy 模块内部使用

Data.Tuplefst :: (a,b) -> afst (x,_) = xsnd :: (a,b) -> bsnd (_,y) = ycurry :: ((a, b) -> c) -> a -> b -> ccur

ParsecParsec是一个词法及语法分析器。匹配字符与字符串Prelude Text.Parsec> parseTest anyChar "a"'a'Prelude Text.Parsec> parseTest (char 'a') "a"'a'Prelude Text.Parsec> parseTest (satisfy (=='a')) "a"'a'Prelude Text.Pa

Bifunctorclass Bifunctor p where bimap :: (a -> b) -> (c -> d) -> p a c -> p b d bimap f g = first f . second g first :: (a -> b) -> p a c -> p b c first f = bimap f id second :: (b -> c) -> p

组合子 1Prelude Text.Parsec Text.Parsec.String> parseTest (count 3 (char 'a')) "aaa""aaa"Prelude Text.Parsec Text.Parsec.String> parseTest (between (char '(') (char ')') anyChar) "(3)"'3'Prelude Text.

preview, reviewPrelude Control.Lens> view _Left (Left "abc")"abc"Prelude Control.Lens> view _Right (Right "abc")"abc"Prelude Control.Lens> view _Just (Just "abc")"abc"Prelude Control.Lens> previe

Applicative Functor

Profunctorclass Profunctor p where dimap :: (a -> b) -> (c -> d) -> p b c -> p a d dimap f g = lmap f . rmap g lmap :: (a -> b) -> p b c -> p a c lmap f = dimap f id rmap :: (b -> c) -> p a b -

Applicative Parsing使用 Applicative 式的 Parser。 包括使用 (<>),(<\*>),(<>), (<\*>), (<), (<*), (*>), (<|>), many 等运算符。应用实例1import Control.Monadimport Text.Parsecimport Control.Applicative hiding ((<|>))numb

Function, Monad, Arrowf :: Int -> (Int, Int)f = \x -> let y = 2 * x z1 = y + 3 z2 = y - 5 in (z1, z2)-- ghci> f 10-- (23, 15)fM :: Int -> Identity (Int, Int)fM = \x -> do y <- re

安装 conduit$ cabal install conduitInstalled conduit-1.3.0.3Prelude&gt; import ConduitPrelude Conduit&gt; ConduitConduit 是一个处理流的库。Prelude Conduit&gt; :{Prelude Conduit| print $ runCo...

Data.Treedata Tree a = Node { rootLabel :: a, subForest :: Forest a } deriving (Eq, Read, Show)type Forest a = [Tree a]Data.Tree 是一种非空（存在根节点），可以有无限分支，每个节点均可有多路分支的Tree类型。...

Divisibleclass Contravariant f =&gt; Divisible f where divide :: (a -&gt; (b, c)) -&gt; f b -&gt; f c -&gt; f a conquer :: f adivided :: Divisible f =&gt; f a -&gt; f b -&gt; f (a, b)divi...

Dicidableclass Divisible f =&gt; Decidable f where lose :: (a -&gt; Void) -&gt; f a choose :: (a -&gt; Either b c) -&gt; f b -&gt; f c -&gt; f alost :: Decidable f =&gt; f Voidlost = lose i...

Prisms{-# LANGUAGE TemplateHaskell, RankNTypes #-}import Control.Lensdata NewTask = SimpleTask String | HarderTask String Int | CompoundTask String [NewTask] deriving (Show)makePrism...

手动计算 set mapped 5 [1,2,3]set l b = runIdentity . l (\_ -&gt; Identity b)mapped = sets fmapsets f g = taintedDot (f (untaintedDot g))instance Settable Identity where untainted = runIdentity ...

Data.Aeson安装 aeson$ cabal install aesonInstalled aeson-1.2.3.0Prelude&gt; :m +Data.AesonPrelude Data.Aeson&gt; Data.Aeson 是一个处理 JSON 数据的库。处理 Person{-# LANGUAGE DeriveGeneric, Overlo...

Gtk2Hs$ brew cask install xquartz$ brew install glib cairo gtk gettext fontconfig freetype$ export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig:$ cabal install alex happy$ cabal install gtk2hs-bui...

安装 HDBC-Sqlite3$ cabal install HDBC-Sqlite3Installed HDBC-sqlite3-2.3.3.1Prelude&gt; :m Database.HDBC Database.HDBC.Sqlite3Prelude Database.HDBC Database.HDBC.Sqlite3&gt;DB 操作Prelude Da...

YesodYesod 是一个使用 Haskell 语言的 Web 框架。安装 Yesod首先更新 Haskell Platform 到最新版 （Yesod 依赖的库非常多，版本不一致的话很容易安装失败）$ cabal install yesodInstalled yesod-1.4.5Hello World-- helloworld.hs{-# LA...

Distributiveclass Functor g =&gt; Distributive g where distribute :: Functor f =&gt; f (g a) -&gt; g (f a) distribute = collect id collect :: Functor f =&gt; (a -&gt; g b) -&gt; f a -...

Biapplicativeclass Bifunctor p =&gt; Biapplicative p where bipure :: a -&gt; b -&gt; p a b (&lt;&lt;*&gt;&gt;) :: p (a -&gt; b) (c -&gt; d) -&gt; p a c -&gt; p b d (*&gt;&gt;) :: p a b -&g

Bitraversableclass (Bifunctor t, Bifoldable t) =&gt; Bitraversable t where bitraverse :: Applicative f =&gt; (a -&gt; f c) -&gt; (b -&gt; f d) -&gt; t a b -&gt; f (t c d) bitraverse f g = bise...

ixPrelude Control.Lens&gt; [1,2,3] ^? ix 1Just 2Prelude Control.Lens&gt; [1,2,3] ^?! ix 12Prelude Control.Lens&gt; [1,2,3] &amp; (ix 1) .~ 20[1,20,3]atrelude Control.Lens&gt; import q...

fix 函数fix 是一个在 Data.Function 模块中定义的函数，它是对于递归的封装，可以用于定义不动点函数。fix :: (a -&gt; a) -&gt; afix f = let x = f x in xfix 函数的定义使用了递归绑定，比较难以理解：fix f= let x = f x in x= let x = f x in f x= let x...

lambda演算根据维基百科，lambda演算（英语：lambda calculus，λ-calculus）是一套从数学逻辑中发展，以变量绑定和替换的规则，来研究函数如何抽象化定义、函数如何被应用以及递归的形式系统。lambda项lambda演算由 lambda 项的语言构成。基本的 lambda 项只包含以下三种： 语法 名称 描述 Haskell语言中的...

reqreq 是一个好用，类型安全，可扩展，上层的HTTP客户端的库。$ cabal install reqInstalled req-1.1.0Prelude&gt; :m +Network.HTTP.ReqPrelude Network.HTTP.Req&gt; 官方示例{-# LANGUAGE OverloadedStrings, DeriveGeneric...

Data.VectorConstructionPrelude V&gt; import Data.Vector as VPrelude V&gt; V.empty[]Prelude V&gt; V.singleton 1[1]Prelude V&gt; V.replicate 5 1[1,1,1,1,1]Prelude V&gt; generate 5 (+1)[1...

手动计算（view, over, set, to, _1）view l = getConst . l Constover l f = runIdentity . l (Identity . f)set l b = runIdentity . l (\_ -&gt; Identity b)to k = dimap k (contramap k)instance Field1 ...

Parser 类型data ParsecT s u m atype Parsec s u = ParsecT s u Identitytype Parser = Parsec String ()data ParsecT s u m a ParsecT 带四个类型参数：数据流类型 s，用户状态类型 u，底层Monad类型 m，返回类型 a。 ParsecT 是一个Monad转...