2f6edad · ikoHSE/sc-lectures

git.iko.soy/ikoHSE/sc-lectures

Added lecture 3

commit2f6edad65028999e4910d512a8c940780f9c237a authoriko <ilyakooo0@gmail.com> dateWed 1 Apr 2020, 23:35 (7 years ago) parent73c1beb

10 files changed+1656−167

compare with master

unifiedsplit

1.html+30−30 2.html+61−55 2.md+23−18 3.html+526−54 3.md+775−1 README.md+11−4 build.sh+1−1 highlight.theme+225 reveal.js/css/theme/source/superblack.scss+2−2 reveal.js/css/theme/superblack.css+2−2

1.html+30−30

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2.html+61−55

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8787

@@ -450,14 +450,14 @@

450450<div class="sourceCode" id="cb75"><pre class="sourceCode java fragment"><code class="sourceCode java"><a href="#cb75-1"></a>m.get("five");

451451<a href="#cb75-2"></a>// null</code></pre></div>

452452<div class="sourceCode" id="cb76"><pre class="sourceCode java fragment"><code class="sourceCode java"><a href="#cb76-1"></a>class TreeMap<K,V> {

453−<a href="#cb76-2"></a> V get(Object key) {

453+<a href="#cb76-2"></a> V get(K key) {

454454<a href="#cb76-3"></a> ...</code></pre></div>

455455Неявный контекст ошибки ВЕЗДЕ.

456456</section>

457457<section class="slide level1">

458458

459459<div class="sourceCode" id="cb77"><pre class="sourceCode java"><code class="sourceCode java"><a href="#cb77-1"></a>class TreeMap<K,V> {

460−<a href="#cb77-2"></a> Pair<V, Boolean> get(Object key) {

460+<a href="#cb77-2"></a> Pair<V, Boolean> get(K key) {

461461<a href="#cb77-3"></a> ...</code></pre></div>

462462<div class="sourceCode" id="cb78"><pre class="sourceCode java fragment"><code class="sourceCode java"><a href="#cb78-1"></a>Pair<Integer, Boolean> result = m.get("one");

463463<a href="#cb78-2"></a>

@@ -479,7 +479,7 @@

479479<section class="slide level1">

480480

481481<div class="sourceCode" id="cb80"><pre class="sourceCode java"><code class="sourceCode java"><a href="#cb80-1"></a>class TreeMap<K,V> {

482−<a href="#cb80-2"></a> V get(Object key) throws NoElementException {

482+<a href="#cb80-2"></a> V get(K key) throws NoElementException {

483483<a href="#cb80-3"></a> ...</code></pre></div>

484484<div class="sourceCode" id="cb81"><pre class="sourceCode java fragment"><code class="sourceCode java"><a href="#cb81-1"></a>try {

485485<a href="#cb81-2"></a> print(m.get("five"));

@@ -493,7 +493,7 @@

493493<div class="sourceCode" id="cb82"><pre class="sourceCode java"><code class="sourceCode java"><a href="#cb82-1"></a>class Optional<T> {

494494<a href="#cb82-2"></a> ...</code></pre></div>

495495<div class="sourceCode" id="cb83"><pre class="sourceCode java fragment"><code class="sourceCode java"><a href="#cb83-1"></a>class TreeMap<K,V> {

496−<a href="#cb83-2"></a> Optional<V> get(Object key) {

496+<a href="#cb83-2"></a> Optional<V> get(K key) {

497497<a href="#cb83-3"></a> ...</code></pre></div>

498498</section>

499499<section class="slide level1">

@@ -583,20 +583,26 @@

583583<div class="sourceCode" id="cb108"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb108-1"></a>class Functor f where

584584<a href="#cb108-2"></a> fmap :: (a -> b) -> f a -> f b</code></pre></div>

585585<div class="sourceCode" id="cb109"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb109-1"></a>class Functor [] where

586−<a href="#cb109-2"></a> fmap _ [] = []

587−<a href="#cb109-3"></a> fmap f (x : xs) = f x : fmap f xs</code></pre></div>

588−<div class="sourceCode" id="cb110"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb110-1"></a>class Functor [] where

589−<a href="#cb110-2"></a> fmap :: (a -> b) -> [a] -> [b]

590−<a href="#cb110-3"></a> fmap _ [] = []

591−<a href="#cb110-4"></a> fmap f (x : xs) = f x : fmap f xs</code></pre></div>

592−<div class="sourceCode" id="cb111"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb111-1"></a>class Functor Maybe where

593−<a href="#cb111-2"></a> fmap :: (a -> b) -> Maybe a -> Maybe b

594−<a href="#cb111-3"></a> fmap _ Nothing = Nothing

595−<a href="#cb111-4"></a> fmap f (Just x) = Just (f x)</code></pre></div>

596−<div class="sourceCode" id="cb112"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb112-1"></a>class Functor (Either e) where

597−<a href="#cb112-2"></a> fmap :: (a -> b) -> Either e a -> Either e b

598−<a href="#cb112-3"></a> fmap _ (Left e) = Left e

599−<a href="#cb112-4"></a> fmap f (Just x) = Just (f x)</code></pre></div>

586+<a href="#cb109-2"></a> fmap :: (a -> b) -> [a] -> [b]

587+<a href="#cb109-3"></a> fmap _ [] = []

588+<a href="#cb109-4"></a> fmap f (x : xs) = f x : fmap f xs</code></pre></div>

589+<div class="sourceCode" id="cb110"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb110-1"></a>class Functor Maybe where

590+<a href="#cb110-2"></a> fmap :: (a -> b) -> Maybe a -> Maybe b

591+<a href="#cb110-3"></a> fmap _ Nothing = Nothing

592+<a href="#cb110-4"></a> fmap f (Just x) = Just (f x)</code></pre></div>

593+<div class="sourceCode" id="cb111"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb111-1"></a>class Functor (Either e) where

594+<a href="#cb111-2"></a> fmap :: (a -> b) -> Either e a -> Either e b

595+<a href="#cb111-3"></a> fmap _ (Left e) = Left e

596+<a href="#cb111-4"></a> fmap f (Right x) = Right (f x)</code></pre></div>

597+</section>

598+<section class="slide level1">

599+

600+<div class="sourceCode" id="cb112"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb112-1"></a>updateAccount :: Account -> Card -> Account

601+<a href="#cb112-2"></a>makePayment :: Card -> Amount -> Either PaymentError Card

602+<a href="#cb112-3"></a>

603+<a href="#cb112-4"></a>newAcccount :: Either PaymentError Account

604+<a href="#cb112-5"></a>newAcccount =

605+<a href="#cb112-6"></a> fmap (updateAccount account) (makePayment card (RUB 150))</code></pre></div>

600606</section>

601607<section class="slide level1">

602608

@@ -604,7 +610,7 @@

604610<a href="#cb113-2"></a> fmap :: (a -> b) -> f a -> f b</code></pre></div>

605611<div class="sourceCode" id="cb114"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb114-1"></a>class Functor (x ->) where

606612<a href="#cb114-2"></a> fmap :: (a -> b) -> (x -> a) -> (x -> b)

607−<a href="#cb114-3"></a> fmap (f :: a -> b) (g :: x -> a) = \x -> f (g x)</code></pre></div>

613+<a href="#cb114-3"></a> fmap (f :: a -> b) (g :: x -> a) = \(u :: x) -> f (g u)</code></pre></div>

608614<div class="sourceCode" id="cb115"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb115-1"></a> fmap (f :: a -> b) (g :: x -> a) = f . g</code></pre></div>

609615<div class="sourceCode" id="cb116"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb116-1"></a> fmap = (.)</code></pre></div>

610616</section>

@@ -612,10 +618,10 @@

612618

613619<h2 id="functor-monoid">Functor + Monoid</h2>

614620<h2 id="alternative">= Alternative!</h2>

615−<div class="sourceCode" id="cb117"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb117-1"></a>foo :: f a -> f a -> f a</code></pre></div>

616−<div class="sourceCode" id="cb118"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb118-1"></a>class Monoid s where

617−<a href="#cb118-2"></a> (<>) :: s -> s -> s

618−<a href="#cb118-3"></a> mempty :: s</code></pre></div>

621+<div class="sourceCode" id="cb117"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb117-1"></a>class Monoid s where

622+<a href="#cb117-2"></a> (<>) :: s -> s -> s

623+<a href="#cb117-3"></a> mempty :: s</code></pre></div>

624+<div class="sourceCode" id="cb118"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb118-1"></a>foo :: f a -> f a -> f a</code></pre></div>

619625<div class="sourceCode" id="cb119"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb119-1"></a>class Functor f => Alternative f where

620626<a href="#cb119-2"></a> (<|>) :: f a -> f a -> f a

621627<a href="#cb119-3"></a> empty :: f a</code></pre></div>

@@ -627,13 +633,13 @@

627633<a href="#cb120-3"></a> empty :: f a</code></pre></div>

628634<div class="sourceCode" id="cb121"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb121-1"></a>instance Alternative Maybe where

629635<a href="#cb121-2"></a> (Just x) <|> _ = Just x

630−<a href="#cb121-3"></a> _ <|> y = y

636+<a href="#cb121-3"></a> Nothing <|> y = y

631637<a href="#cb121-4"></a>

632638<a href="#cb121-5"></a> empty = Nothing</code></pre></div>

633639<div class="sourceCode" id="cb122"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb122-1"></a>Just 42 <|> Just 69

634640<a href="#cb122-2"></a>-- Just 42</code></pre></div>

635641<div class="sourceCode" id="cb123"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb123-1"></a>Nothing <|> Just 69

636−<a href="#cb123-2"></a>-- Nothing</code></pre></div>

642+<a href="#cb123-2"></a>-- Just 69</code></pre></div>

637643</section>

638644<section class="slide level1">

639645

2.md+23−18

@@ -572,7 +572,7 @@ m.get("five");

572572

573573```{ .java .fragment }

574574class TreeMap<K,V> {

575− V get(Object key) {

575+ V get(K key) {

576576 ...

577577```

578578

@@ -582,7 +582,7 @@ class TreeMap<K,V> {

582582

583583```{ .java }

584584class TreeMap<K,V> {

585− Pair<V, Boolean> get(Object key) {

585+ Pair<V, Boolean> get(K key) {

586586 ...

587587```

588588

@@ -612,7 +612,7 @@ if (result.second()) {

612612

613613```{ .java }

614614class TreeMap<K,V> {

615− V get(Object key) throws NoElementException {

615+ V get(K key) throws NoElementException {

616616 ...

617617```

618618

@@ -634,7 +634,7 @@ class Optional<T> {

634634

635635```{ .java .fragment }

636636class TreeMap<K,V> {

637− Optional<V> get(Object key) {

637+ Optional<V> get(K key) {

638638 ...

639639```

640640

@@ -798,12 +798,6 @@ class Functor f where

798798 fmap :: (a -> b) -> f a -> f b

799799```

800800

801−```{ .haskell .fragment }

802−class Functor [] where

803− fmap _ [] = []

804− fmap f (x : xs) = f x : fmap f xs

805−```

806−

807801```{ .haskell .fragment }

808802class Functor [] where

809803 fmap :: (a -> b) -> [a] -> [b]

@@ -822,7 +816,18 @@ class Functor Maybe where

822816class Functor (Either e) where

823817 fmap :: (a -> b) -> Either e a -> Either e b

824818 fmap _ (Left e) = Left e

825− fmap f (Just x) = Just (f x)

819+ fmap f (Right x) = Right (f x)

820+```

821+

822+---

823+

824+```{ .haskell }

825+updateAccount :: Account -> Card -> Account

826+makePayment :: Card -> Amount -> Either PaymentError Card

827+

828+newAcccount :: Either PaymentError Account

829+newAcccount =

830+ fmap (updateAccount account) (makePayment card (RUB 150))

826831```

827832

828833---

@@ -835,7 +840,7 @@ class Functor f where

835840```{ .haskell .fragment }

836841class Functor (x ->) where

837842 fmap :: (a -> b) -> (x -> a) -> (x -> b)

838− fmap (f :: a -> b) (g :: x -> a) = \x -> f (g x)

843+ fmap (f :: a -> b) (g :: x -> a) = \(u :: x) -> f (g u)

839844```

840845

841846```{ .haskell .fragment }

@@ -852,16 +857,16 @@ class Functor (x ->) where

852857## [= Alternative!]{.fragment}

853858

854859

855−```{ .haskell .fragment }

856−foo :: f a -> f a -> f a

857−```

858−

859860```{ .haskell .fragment }

860861class Monoid s where

861862 (<>) :: s -> s -> s

862863 mempty :: s

863864```

864865

866+```{ .haskell .fragment }

867+foo :: f a -> f a -> f a

868+```

869+

865870```{ .haskell .fragment }

866871class Functor f => Alternative f where

867872 (<|>) :: f a -> f a -> f a

@@ -879,7 +884,7 @@ class Functor f => Alternative f where

879884```{ .haskell .fragment }

880885instance Alternative Maybe where

881886 (Just x) <|> _ = Just x

882− _ <|> y = y

887+ Nothing <|> y = y

883888

884889 empty = Nothing

885890```

@@ -891,7 +896,7 @@ Just 42 <|> Just 69

891896

892897```{ .haskell .fragment }

893898Nothing <|> Just 69

894−-- Nothing

899+-- Just 69

895900```

896901

897902---

3.html+526−54

@@ -47,41 +47,41 @@

4747 }

4848 pre.numberSource { margin-left: 3em; border-left: 1px solid #7a7c7d; padding-left: 4px; }

4949 div.sourceCode

50− { color: #cfcfc2; background-color: #232629; }

50+ { color: #ffffff; background-color: #000000; }

5151 @media screen {

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8787

@@ -112,31 +112,46 @@

112112 <div class="slides">

113113

114114

115−<section id="библиотека-про-математику" class="slide level3">

116−<h3>Библиотека про математику</h3>

115+<section>

116+<section id="функциональное-программирование" class="title-slide slide level1">

117+<h1>Функциональное программирование</h1>

118+

119+</section>

120+<section id="напоминалочка" class="slide level2">

121+<h2>Напоминалочка</h2>

122+<div class="sourceCode" id="cb1"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb1-1"></a>class Functor f where

123+<a href="#cb1-2"></a> fmap :: (a -> b) -> f a -> f b</code></pre></div>

124+<div class="sourceCode" id="cb2"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb2-1"></a>class Functor f => Alternative f where

125+<a href="#cb2-2"></a> (<|>) :: f a -> f a -> f a

126+<a href="#cb2-3"></a> empty :: f a</code></pre></div>

127+</section>

128+<section id="библиотека-про-математику" class="slide level2">

129+<h2>Библиотека про математику</h2>

117130<h4 id="на-джаве">(на джаве)</h4>

118−<div class="sourceCode" id="cb1"><pre class="sourceCode java fragment"><code class="sourceCode java"><a href="#cb1-1"></a>static int add(int x, int y) {

119−<a href="#cb1-2"></a> return x + y;

120−<a href="#cb1-3"></a>}</code></pre></div>

131+<div class="sourceCode" id="cb3"><pre class="sourceCode java fragment"><code class="sourceCode java"><a href="#cb3-1"></a>static int add(int x, int y) {

132+<a href="#cb3-2"></a> return x + y;

133+<a href="#cb3-3"></a>}</code></pre></div>

121134“Нам для сертификации надо чтобы каждая функция логировала свой вызов.”

122135</section>

123−<section id="вариант-1" class="slide level3">

124−<h3>Вариант 1</h3>

125−<div class="sourceCode" id="cb2"><pre class="sourceCode java fragment"><code class="sourceCode java"><a href="#cb2-1"></a>static int add(int x, int y) {

126−<a href="#cb2-2"></a> log += "add";

127−<a href="#cb2-3"></a> return x + y;

128−<a href="#cb2-4"></a>}</code></pre></div>

136+<section class="slide level2">

137+

138+<h3 id="вариант-1">Вариант 1</h3>

139+<div class="sourceCode" id="cb4"><pre class="sourceCode java fragment"><code class="sourceCode java"><a href="#cb4-1"></a>static int add(int x, int y) {

140+<a href="#cb4-2"></a> log += "add";

141+<a href="#cb4-3"></a> return x + y;

142+<a href="#cb4-4"></a>}</code></pre></div>

129143<ol type="1">

130144<li class="fragment">Неявная зависимость</li>

131145<li class="fragment">Невозможно рефакторить</li>

132146<li class="fragment">Почему функция для складывания чисел умеет логи?</li>

133147</ol>

134148</section>

135−<section id="вариант-2" class="slide level3">

136−<h3>Вариант 2</h3>

137−<div class="sourceCode" id="cb3"><pre class="sourceCode java fragment"><code class="sourceCode java"><a href="#cb3-1"></a>static Pair<Integer, String> add(int x, int y, string log) {

138−<a href="#cb3-2"></a> return new Pair(x + y, log + "add");

139−<a href="#cb3-3"></a>}</code></pre></div>

149+<section class="slide level2">

150+

151+<h3 id="вариант-2">Вариант 2</h3>

152+<div class="sourceCode" id="cb5"><pre class="sourceCode java fragment"><code class="sourceCode java"><a href="#cb5-1"></a>static Pair<Integer, String> add(int x, int y, string log) {

153+<a href="#cb5-2"></a> return new Pair(x + y, log + "add");

154+<a href="#cb5-3"></a>}</code></pre></div>

140155<ol type="1">

141156<li class="fragment"><del>Неявная зависимость</del></li>

142157<li class="fragment"><del>Невозможно рефакторить</del></li>

@@ -144,12 +159,13 @@

144159<li class="fragment">Почему функция для складывания чисел умеет логи?</li>

145160</ol>

146161</section>

147−<section id="вариант-ооп" class="slide level3">

148−<h3>Вариант ООП</h3>

149−<div class="sourceCode" id="cb4"><pre class="sourceCode java fragment"><code class="sourceCode java"><a href="#cb4-1"></a>static int add(int x, int y, Logger log) {

150−<a href="#cb4-2"></a> Logger.log("add");

151−<a href="#cb4-3"></a> return x + y;

152−<a href="#cb4-4"></a>}</code></pre></div>

162+<section class="slide level2">

163+

164+<h3 id="вариант-ооп">Вариант ООП</h3>

165+<div class="sourceCode" id="cb6"><pre class="sourceCode java fragment"><code class="sourceCode java"><a href="#cb6-1"></a>static int add(int x, int y, Logger log) {

166+<a href="#cb6-2"></a> Logger.log("add");

167+<a href="#cb6-3"></a> return x + y;

168+<a href="#cb6-4"></a>}</code></pre></div>

153169<ol type="1">

154170<li class="fragment"><del>Неявная зависимость</del></li>

155171<li class="fragment"><del>Невозможно рефакторить</del></li>

@@ -157,10 +173,466 @@

157173<li class="fragment"><del>Почему функция для складывания чисел умеет логи?</del></li>

158174</ol>

159175</section>

160−<section class="slide level3">

176+<section class="slide level2">

177+

178+<div class="sourceCode" id="cb7"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb7-1"></a>add :: Int -> Int -> (Int, String)

179+<a href="#cb7-2"></a>add x y = (x + y, "add " + show x + show y)</code></pre></div>

180+Неудобно программировать

181+<div class="sourceCode" id="cb8"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb8-1"></a>add :: Int -> Int -> Int

182+<a href="#cb8-2"></a>times :: Int -> Int -> Int

183+<a href="#cb8-3"></a>

184+<a href="#cb8-4"></a>add8AndDouble :: Int -> Int

185+<a href="#cb8-5"></a>add8AndDouble = times 2 . add 8</code></pre></div>

186+</section>

187+<section class="slide level2">

188+

189+<div class="sourceCode" id="cb9"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb9-1"></a>add :: Int -> Int -> (Int, String)

190+<a href="#cb9-2"></a>times :: Int -> Int -> (Int, String)</code></pre></div>

191+<div class="sourceCode" id="cb10"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb10-1"></a>add8AndDouble :: Int -> (Int, String)

192+<a href="#cb10-2"></a>add8AndDouble x = (y2, log1 <> log2)

193+<a href="#cb10-3"></a> where

194+<a href="#cb10-4"></a> (y1, log1) = add 8 x

195+<a href="#cb10-5"></a> (y2, log2) = times 2 y1</code></pre></div>

196+<img data-src="images/ohno.png" class="fragment" height="200" />

197+<div class="sourceCode" id="cb11"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb11-1"></a>add8AndDouble :: Int -> Int

198+<a href="#cb11-2"></a>add8AndDouble = times 2 . add 8</code></pre></div>

199+</section>

200+<section class="slide level2">

201+

202+<div class="sourceCode" id="cb12"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb12-1"></a>data WithLog a = WithLog a String</code></pre></div>

203+<div class="sourceCode" id="cb13"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb13-1"></a>add :: Int -> Int -> WithLog Int

204+<a href="#cb13-2"></a>times :: Int -> Int -> WithLog Int</code></pre></div>

205+<div class="sourceCode" id="cb14"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb14-1"></a>add8AndDouble :: Int -> WithLog Int

206+<a href="#cb14-2"></a>add8AndDouble = times 2 `magic` add 8</code></pre></div>

207+<div class="sourceCode" id="cb15"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb15-1"></a>magic ::

208+<a href="#cb15-2"></a> (Int -> WithLog Int) ->

209+<a href="#cb15-3"></a> (Int -> WithLog Int) ->

210+<a href="#cb15-4"></a> (Int -> WithLog Int)</code></pre></div>

211+<div class="sourceCode" id="cb16"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb16-1"></a>magic f g x1 = WithLog x3 (log1 <> log2)

212+<a href="#cb16-2"></a> where

213+<a href="#cb16-3"></a> (WithLog x2 log1) = g x1

214+<a href="#cb16-4"></a> (WithLog x3 log2) = f x2</code></pre></div>

215+</section>

216+<section class="slide level2">

217+

218+<div class="sourceCode" id="cb17"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb17-1"></a>magic ::

219+<a href="#cb17-2"></a> (Int -> WithLog Int) ->

220+<a href="#cb17-3"></a> (Int -> WithLog Int) ->

221+<a href="#cb17-4"></a> (Int -> WithLog Int)</code></pre></div>

222+<div class="sourceCode" id="cb18"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb18-1"></a>(<=<) ::

223+<a href="#cb18-2"></a> (Int -> WithLog Int) ->

224+<a href="#cb18-3"></a> (Int -> WithLog Int) ->

225+<a href="#cb18-4"></a> (Int -> WithLog Int)</code></pre></div>

226+<div class="sourceCode" id="cb19"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb19-1"></a>add8AndDouble :: Int -> WithLog Int

227+<a href="#cb19-2"></a>add8AndDouble = times 2 <=< add 8</code></pre></div>

228+</section>

229+<section class="slide level2">

230+

231+<div class="sourceCode" id="cb20"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb20-1"></a>factor :: Int -> WithLog [Int]

232+<a href="#cb20-2"></a>

233+<a href="#cb20-3"></a>sum :: [Int] -> WithLog Int</code></pre></div>

234+<div class="sourceCode" id="cb21"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb21-1"></a>sumFactors :: Int -> WithLog [Int]

235+<a href="#cb21-2"></a>sumFactors = sum <=< factor -- Doesn't work :(</code></pre></div>

236+<div class="sourceCode" id="cb22"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb22-1"></a>(<=<) ::

237+<a href="#cb22-2"></a> (Int -> WithLog Int) ->

238+<a href="#cb22-3"></a> (Int -> WithLog Int) ->

239+<a href="#cb22-4"></a> (Int -> WithLog Int)</code></pre></div>

240+<div class="sourceCode" id="cb23"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb23-1"></a>(<=<) ::

241+<a href="#cb23-2"></a> (b -> WithLog c ) ->

242+<a href="#cb23-3"></a> (a -> WithLog b ) ->

243+<a href="#cb23-4"></a> (a -> WithLog c )</code></pre></div>

244+<div class="sourceCode" id="cb24"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb24-1"></a>(.) ::

245+<a href="#cb24-2"></a> (b -> c ) ->

246+<a href="#cb24-3"></a> (a -> b ) ->

247+<a href="#cb24-4"></a> (a -> c )</code></pre></div>

248+</section>

249+<section class="slide level2">

250+

251+<div class="sourceCode" id="cb25"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb25-1"></a>getCoffee :: Order -> Maybe Coffee

252+<a href="#cb25-2"></a>payForCoffee :: Coffee -> Maybe Payment</code></pre></div>

253+<div class="sourceCode" id="cb26"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb26-1"></a>buyCoffee :: Order -> Maybe Payment

254+<a href="#cb26-2"></a>buyCoffee = payForCoffee <=< getCoffee</code></pre></div>

255+<div class="sourceCode" id="cb27"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb27-1"></a>getCoffee :: Order -> Either CoffeeError Coffee

256+<a href="#cb27-2"></a>payForCoffee :: Coffee -> Either CoffeeError Payment</code></pre></div>

257+<div class="sourceCode" id="cb28"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb28-1"></a>buyCoffee :: Order -> Either CoffeeError Payment

258+<a href="#cb28-2"></a>buyCoffee = payForCoffee <=< getCoffee</code></pre></div>

259+<div class="sourceCode" id="cb29"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb29-1"></a>(<=<) ::

260+<a href="#cb29-2"></a> Composable m =>

261+<a href="#cb29-3"></a> (b -> m c) ->

262+<a href="#cb29-4"></a> (a -> m b) ->

263+<a href="#cb29-5"></a> (a -> m c)</code></pre></div>

264+</section>

265+<section class="slide level2">

266+

267+<div class="sourceCode" id="cb30"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb30-1"></a>class Applicative m => Monad m where

268+<a href="#cb30-2"></a> (<=<) :: (b -> m c) -> (a -> m b) -> (a -> m c)</code></pre></div>

269+<div class="sourceCode" id="cb31"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb31-1"></a>instance Monad Maybe where

270+<a href="#cb31-2"></a> (<=<) f g x = case g x of

271+<a href="#cb31-3"></a> Nothing -> Nothing

272+<a href="#cb31-4"></a> Just x2 -> f x2</code></pre></div>

273+<div class="sourceCode" id="cb32"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb32-1"></a>instance Monad (Either e) where

274+<a href="#cb32-2"></a> (<=<) f g x = case g x of

275+<a href="#cb32-3"></a> Left e -> Left e

276+<a href="#cb32-4"></a> Right x2 -> f x2</code></pre></div>

277+<div class="sourceCode" id="cb33"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb33-1"></a>instance Monad WithLog where

278+<a href="#cb33-2"></a> (<=<) f g x = WithLog x3 (log1 <> log2)

279+<a href="#cb33-3"></a> where

280+<a href="#cb33-4"></a> (WithLog x2 log1) = g x1

281+<a href="#cb33-5"></a> (WithLog x3 log2) = f x2</code></pre></div>

282+</section>

283+<section class="slide level2">

284+

285+<h3 id="больше-операторов">Больше операторов!</h3>

286+<div class="sourceCode" id="cb34"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb34-1"></a>(<=<) :: Monad m => (b -> m c) -> (a -> m b) -> (a -> m c)</code></pre></div>

287+<div class="sourceCode" id="cb35"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb35-1"></a>buyCoffee :: Order -> Maybe Payment

288+<a href="#cb35-2"></a>buyCoffee = payForCoffee <=< getCoffee</code></pre></div>

289+<div class="sourceCode" id="cb36"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb36-1"></a>flip :: (a -> b -> c) -> (b -> a -> c)

290+<a href="#cb36-2"></a>flip f b a = f a b</code></pre></div>

291+<div class="sourceCode" id="cb37"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb37-1"></a>(>=>) :: Monad m => (a -> m b) -> (b -> m c) -> (a -> m c)

292+<a href="#cb37-2"></a>(>=>) = flip (<=<)</code></pre></div>

293+<div class="sourceCode" id="cb38"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb38-1"></a>buyCoffee = getCoffee >=> payForCoffee</code></pre></div>

294+</section>

295+<section class="slide level2">

296+

297+<h3 id="маленькое-отступление">Маленькое отступление</h3>

298+<code>f :: () -> a</code> эквивалентно <code>f :: a</code>

299+Потому что у <code>()</code> всего одно значение (<code>()</code>), а любая функция для одинаковых аргументов всегда возвращает одинаковые значения (потому что по-другому невозможно).

300+</section>

301+<section class="slide level2">

302+

303+<div class="sourceCode" id="cb39"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb39-1"></a>(>=>) :: Monad m => (a -> m b) -> (b -> m c) -> (a -> m c)</code></pre></div>

304+<div class="sourceCode" id="cb40"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb40-1"></a>(>>=) :: Monad m => m b -> (b -> m c) -> m c</code></pre></div>

305+<div class="sourceCode" id="cb41"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb41-1"></a>buyCoffee :: Order -> Maybe Payment

306+<a href="#cb41-2"></a>buyCoffee order = getCoffee order >>= payForCoffee</code></pre></div>

307+<div class="sourceCode" id="cb42"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb42-1"></a>maybeBuyCoffee :: Myabe Order -> Maybe Payment

308+<a href="#cb42-2"></a>maybeBuyCoffee order = order >>= buyCoffee</code></pre></div>

309+<div class="sourceCode" id="cb43"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb43-1"></a>(>>=) :: Monad m => m b -> (b -> m c) -> m c</code></pre></div>

310+<div class="sourceCode" id="cb44"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb44-1"></a>(>=>) :: Monad m => (a -> m b) -> (b -> m c) -> (a -> m c)</code></pre></div>

311+<div class="sourceCode" id="cb45"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb45-1"></a> (() -> m b) -> (b -> m c) -> (() -> m c)</code></pre></div>

312+<div class="sourceCode" id="cb46"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb46-1"></a> m b -> (b -> m c) -> m c</code></pre></div>

313+</section>

314+<section class="slide level2">

315+

316+<div class="sourceCode" id="cb47"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb47-1"></a>(>=>) :: Monad m => (a -> m b) -> (b -> m c) -> (a -> m c)</code></pre></div>

317+<div class="sourceCode" id="cb48"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb48-1"></a>(>>=) :: Monad m => m b -> (b -> m c) -> m c

318+<a href="#cb48-2"></a>(>>=) mb f = ( (\() -> mb) >=> f ) ()</code></pre></div>

319+<div class="sourceCode" id="cb49"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb49-1"></a>(>>=) mb f = ( (\() -> mb) >=> f ) ()

320+<a href="#cb49-2"></a>-- () -> m b |

321+<a href="#cb49-3"></a>-- b -> m c

322+<a href="#cb49-4"></a>--

323+<a href="#cb49-5"></a>-- ^-------------------^

324+<a href="#cb49-6"></a>-- () -> m c</code></pre></div>

325+</section>

326+<section class="slide level2">

327+

328+<h3 id="время-раскрыть-ложь">Время раскрыть ложь</h3>

329+<div class="sourceCode" id="cb50"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb50-1"></a>class Applicative m => Monad m where

330+<a href="#cb50-2"></a> (>>=) :: m a -> (a -> m b) -> m b

331+<a href="#cb50-3"></a> return :: a -> m a</code></pre></div>

332+<div class="sourceCode" id="cb51"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb51-1"></a> -- Law:

333+<a href="#cb51-2"></a> ma :: m a

334+<a href="#cb51-3"></a> (ma >>= return) == ma</code></pre></div>

335+<div class="sourceCode" id="cb52"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb52-1"></a> -- Law:

336+<a href="#cb52-2"></a> f :: a -> m b

337+<a href="#cb52-3"></a> (f >=> return) == f</code></pre></div>

338+<code>return</code> – нейтральный элемент по <code>>=></code>

339+<div class="sourceCode" id="cb53"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb53-1"></a> -- Law:

340+<a href="#cb53-2"></a> x :: a

341+<a href="#cb53-3"></a> f :: a -> m b

342+<a href="#cb53-4"></a> (return x >>= f) == f x</code></pre></div>

343+</section>

344+<section class="slide level2">

161345

162−<div class="sourceCode" id="cb5"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"></code></pre></div>

346+<div class="sourceCode" id="cb54"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb54-1"></a>instance Monad Maybe where

347+<a href="#cb54-2"></a> ma >>= f = case ma of

348+<a href="#cb54-3"></a> Nothing -> Nothing

349+<a href="#cb54-4"></a> Just a -> f a

350+<a href="#cb54-5"></a>

351+<a href="#cb54-6"></a> return a = Just a</code></pre></div>

352+<div class="sourceCode" id="cb55"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb55-1"></a>instance Monad (Either e) where

353+<a href="#cb55-2"></a> ma >>= f = case ma of

354+<a href="#cb55-3"></a> Left e -> Left e

355+<a href="#cb55-4"></a> Right a -> f a

356+<a href="#cb55-5"></a>

357+<a href="#cb55-6"></a> return a = Right a</code></pre></div>

358+<div class="sourceCode" id="cb56"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb56-1"></a>instance Monad WithLog where

359+<a href="#cb56-2"></a> (WithLog a log1) >>= f = WithLog b (log1 <> log2)

360+<a href="#cb56-3"></a> where

361+<a href="#cb56-4"></a> WithLog b log2 = f a

362+<a href="#cb56-5"></a>

363+<a href="#cb56-6"></a> return a = WithLog a ""</code></pre></div>

163364</section>

365+<section id="more-monads" class="slide level2">

366+<h2>More Monads!</h2>

367+<div class="sourceCode" id="cb57"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb57-1"></a>type Markup = Int

368+<a href="#cb57-2"></a>

369+<a href="#cb57-3"></a>getCoffee :: Markup -> Order -> Coffee

370+<a href="#cb57-4"></a>payForCoffee :: Markup -> Coffee -> Payment

371+<a href="#cb57-5"></a>

372+<a href="#cb57-6"></a>buyCoffee :: Markup -> Order -> Payment

373+<a href="#cb57-7"></a>buyCoffee markup = payForCoffee markup . getCoffee markup</code></pre></div>

374+<div class="sourceCode" id="cb58"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb58-1"></a>data Reader r a = Reader

375+<a href="#cb58-2"></a> { runReader :: r -> a

376+<a href="#cb58-3"></a> }</code></pre></div>

377+<code>r</code> – то, что у нас в “окружении”.

378+<div class="sourceCode" id="cb59"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb59-1"></a>getCoffee :: Order -> Reader Markup Coffee

379+<a href="#cb59-2"></a>payForCoffee :: Coffee -> Reader Markup Payment</code></pre></div>

380+<div class="sourceCode" id="cb60"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb60-1"></a>payment :: Payment

381+<a href="#cb60-2"></a>payment = runReader (payForCoffee coffee) markup</code></pre></div>

382+</section>

383+<section class="slide level2">

384+

385+<div class="sourceCode" id="cb61"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb61-1"></a>data Reader r a = Reader { runReader :: r -> a }

386+<a href="#cb61-2"></a>

387+<a href="#cb61-3"></a>getCoffee :: Order -> Reader Markup Coffee

388+<a href="#cb61-4"></a>payForCoffee :: Coffee -> Reader Markup Payment</code></pre></div>

389+<div class="sourceCode" id="cb62"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb62-1"></a>buyCoffee :: Order -> Reader Markup Payment

390+<a href="#cb62-2"></a>buyCoffee = payForCoffee <=< getCoffee</code></pre></div>

391+<div class="sourceCode" id="cb63"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb63-1"></a>type PricingEnv = Reader Markup</code></pre></div>

392+<div class="sourceCode" id="cb64"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb64-1"></a>getCoffee :: Order -> PricingEnv Coffee

393+<a href="#cb64-2"></a>payForCoffee :: Coffee -> PricingEnv Payment

394+<a href="#cb64-3"></a>buyCoffee :: Order -> PricingEnv Payment

395+<a href="#cb64-4"></a>buyCoffee = payForCoffee <=< getCoffee</code></pre></div>

396+</section>

397+<section class="slide level2">

398+

399+<div class="sourceCode" id="cb65"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb65-1"></a>data Reader r a = Reader

400+<a href="#cb65-2"></a> { runReader :: r -> a

401+<a href="#cb65-3"></a> }

402+<a href="#cb65-4"></a>

403+<a href="#cb65-5"></a>instance Monad (Reader r) where

404+<a href="#cb65-6"></a> return a = Reader (\_ -> a)

405+<a href="#cb65-7"></a>

406+<a href="#cb65-8"></a> (Reader g) >>= f = Reader ( \r -> runReader (f (g r)) r )</code></pre></div>

407+<div class="sourceCode" id="cb66"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb66-1"></a> (>>=) :: Reader r a -> (a -> Reader r b) -> Reader r b

408+<a href="#cb66-2"></a>

409+<a href="#cb66-3"></a> (Reader g) >>= f = Reader ( \r -> runReader (f (g r)) r )

410+<a href="#cb66-4"></a>-- ^---^

411+<a href="#cb66-5"></a>-- a

412+<a href="#cb66-6"></a>-- ^-------^

413+<a href="#cb66-7"></a>-- Reader r b

414+<a href="#cb66-8"></a>-- ^-----------------^

415+<a href="#cb66-9"></a>-- r -> b</code></pre></div>

416+</section>

417+<section class="slide level2">

418+

419+<div class="sourceCode" id="cb67"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb67-1"></a>type Price = Int

420+<a href="#cb67-2"></a>getCoffeePrice :: Markup -> Coffee -> Price

421+<a href="#cb67-3"></a>getDiscount :: Markup -> Coffee -> Price

422+<a href="#cb67-4"></a>getPayment :: Markup -> Price -> Payment

423+<a href="#cb67-5"></a>

424+<a href="#cb67-6"></a>payForCoffee :: Markup -> Coffee -> Payment

425+<a href="#cb67-7"></a>payForCoffee markup coffee = getPayment markup amount

426+<a href="#cb67-8"></a> where

427+<a href="#cb67-9"></a> coffeePrice = getCoffeePrice markup coffee

428+<a href="#cb67-10"></a> discount = getDiscount markup coffee

429+<a href="#cb67-11"></a> amount = coffeePrice - discount</code></pre></div>

430+<div class="sourceCode" id="cb68"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb68-1"></a>type PricingEnv = Reader Markup

431+<a href="#cb68-2"></a>

432+<a href="#cb68-3"></a>getCoffeePrice :: Coffee -> PricingEnv Price

433+<a href="#cb68-4"></a>getDiscount :: Coffee -> PricingEnv Price

434+<a href="#cb68-5"></a>getPayment :: Price -> PricingEnv Payment

435+<a href="#cb68-6"></a>

436+<a href="#cb68-7"></a>payForCoffee :: Coffee -> PricingEnv Payment

437+<a href="#cb68-8"></a>payForCoffee coffee =

438+<a href="#cb68-9"></a> coffee >>= getCoffeePrice >>= \coffeePrice ->

439+<a href="#cb68-10"></a> coffee >>= getDiscount >>= \discount ->

440+<a href="#cb68-11"></a> getPayment (coffeePrice - discount)</code></pre></div>

441+</section>

442+<section id="do-syntax" class="slide level2">

443+<h2>Do syntax</h2>

444+<div class="sourceCode" id="cb69"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb69-1"></a>bar :: Reader r a

445+<a href="#cb69-2"></a>qux :: a -> Reader r b

446+<a href="#cb69-3"></a>

447+<a href="#cb69-4"></a>foo :: Reader r b

448+<a href="#cb69-5"></a>foo = bar >>= \a -> qux a</code></pre></div>

449+<div class="sourceCode" id="cb70"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb70-1"></a>foo = do

450+<a href="#cb70-2"></a> a <- bar

451+<a href="#cb70-3"></a> qux a</code></pre></div>

452+<div class="sourceCode" id="cb71"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb71-1"></a>foo = do

453+<a href="#cb71-2"></a> a <- bar

454+<a href="#cb71-3"></a> b <- qux a

455+<a href="#cb71-4"></a> return b</code></pre></div>

456+</section>

457+<section class="slide level2">

458+

459+<div class="sourceCode" id="cb72"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb72-1"></a>type PricingEnv = Reader Markup

460+<a href="#cb72-2"></a>

461+<a href="#cb72-3"></a>getCoffeePrice :: Coffee -> PricingEnv Price

462+<a href="#cb72-4"></a>getDiscount :: Coffee -> PricingEnv Price

463+<a href="#cb72-5"></a>getPayment :: Price -> PricingEnv Payment

464+<a href="#cb72-6"></a>

465+<a href="#cb72-7"></a>payForCoffee :: Coffee -> PricingEnv Payment

466+<a href="#cb72-8"></a>payForCoffee coffee =

467+<a href="#cb72-9"></a> coffee >>= getCoffeePrice >>= \coffeePrice ->

468+<a href="#cb72-10"></a> coffee >>= getDiscount >>= \discount ->

469+<a href="#cb72-11"></a> getPayment (coffeePrice - discount)</code></pre></div>

470+<div class="sourceCode" id="cb73"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb73-1"></a>payForCoffee :: Coffee -> PricingEnv Payment

471+<a href="#cb73-2"></a>payForCoffee coffee = do

472+<a href="#cb73-3"></a> coffeePrice <- getCoffeePrice coffee

473+<a href="#cb73-4"></a> discount <- getDiscount coffee

474+<a href="#cb73-5"></a> getPayment (coffeePrice - discount)</code></pre></div>

475+</section>

476+<section id="let-statement" class="slide level2">

477+<h2>Let statement</h2>

478+<div class="sourceCode" id="cb74"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb74-1"></a>payForCoffee :: Coffee -> PricingEnv Payment

479+<a href="#cb74-2"></a>payForCoffee coffee = do

480+<a href="#cb74-3"></a> coffeePrice <- getCoffeePrice coffee

481+<a href="#cb74-4"></a> discount <- getDiscount coffee

482+<a href="#cb74-5"></a> getPayment (coffeePrice - discount)</code></pre></div>

483+<div class="sourceCode" id="cb75"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb75-1"></a>payForCoffee :: Coffee -> PricingEnv Payment

484+<a href="#cb75-2"></a>payForCoffee coffee = do

485+<a href="#cb75-3"></a> coffeePrice <- getCoffeePrice coffee

486+<a href="#cb75-4"></a> discount <- getDiscount coffee

487+<a href="#cb75-5"></a> let amount = coffeePrice - discount

488+<a href="#cb75-6"></a> getPayment amount</code></pre></div>

489+</section>

490+<section class="slide level2">

491+

492+<div class="sourceCode" id="cb76"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb76-1"></a>type PricingEnv = Reader Markup

493+<a href="#cb76-2"></a>type Price = Int

494+<a href="#cb76-3"></a>

495+<a href="#cb76-4"></a>data Coffee = Coffee { getCoffeePrice :: Price }

496+<a href="#cb76-5"></a>

497+<a href="#cb76-6"></a>getCoffeePrice :: Coffee -> PricingEnv Price</code></pre></div>

498+<div class="sourceCode" id="cb77"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb77-1"></a>data Reader r a = Reader { runReader :: r -> a}</code></pre></div>

499+<div class="sourceCode" id="cb78"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb78-1"></a>ask :: Reader r r

500+<a href="#cb78-2"></a>ask = Reader (\r -> r)</code></pre></div>

501+<div class="sourceCode" id="cb79"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb79-1"></a>getCoffeePrice :: Coffee -> PricingEnv Price

502+<a href="#cb79-2"></a>getCoffeePrice coffee = do

503+<a href="#cb79-3"></a> markup <- ask

504+<a href="#cb79-4"></a> let coffePrice = getCoffeePrice coffee

505+<a href="#cb79-5"></a> return (coffee + markup)</code></pre></div>

506+</section>

507+<section class="slide level2">

508+

509+<div class="sourceCode" id="cb80"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb80-1"></a>data Order = Order { orderCoffee :: Coffee, orderId :: Int }</code></pre></div>

510+<div class="sourceCode" id="cb81"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb81-1"></a>createOrder :: Coffee -> Order</code></pre></div>

511+Откуда брать <code>orderId</code>?

512+<div class="sourceCode" id="cb82"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb82-1"></a>createOrder :: Coffee -> Reader Int Order

513+<a href="#cb82-2"></a>createOrder coffee = do

514+<a href="#cb82-3"></a> newId <- ask

515+<a href="#cb82-4"></a> return (Order coffee newId)</code></pre></div>

516+🎉

517+<div class="sourceCode" id="cb83"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb83-1"></a>createOrders :: [Coffee] -> Reader Int [Order]</code></pre></div>

518+<div class="sourceCode" id="cb84"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb84-1"></a>mapM :: (Monad m) => (a -> m b) -> [a] -> m [b]</code></pre></div>

519+<div class="sourceCode" id="cb85"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb85-1"></a>createOrders = mapM createOrder</code></pre></div>

520+</section>

521+<section class="slide level2">

522+

523+<div class="sourceCode" id="cb86"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb86-1"></a>createOrders :: [Coffee] -> Reader Int [Order]

524+<a href="#cb86-2"></a>createOrders = mapM createOrder</code></pre></div>

525+Все <code>id</code> будут одинаковые.

526+<code>Reader</code> эквивалентно глобальной константе.

527+Айдишники – скорее глобальная переменная.

528+– Но у нас же нет переменных!

529+– Да, нет!

530+</section>

531+<section id="state" class="slide level2">

532+<h2>State!</h2>

533+<div class="sourceCode" id="cb87"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb87-1"></a>data State s a = ... -- s -- само состояние

534+<a href="#cb87-2"></a>

535+<a href="#cb87-3"></a>get :: State s s

536+<a href="#cb87-4"></a>put :: s -> State s ()</code></pre></div>

537+<div class="sourceCode" id="cb88"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb88-1"></a>data State s a = State { runState :: s -> (a, s) }

538+<a href="#cb88-2"></a>

539+<a href="#cb88-3"></a>get :: State s s

540+<a href="#cb88-4"></a>get = State (\s -> (s, s))

541+<a href="#cb88-5"></a>

542+<a href="#cb88-6"></a>put :: s -> State s ()

543+<a href="#cb88-7"></a>put s = State (\_ -> ((), s))</code></pre></div>

544+</section>

545+<section class="slide level2">

546+

547+<div class="sourceCode" id="cb89"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb89-1"></a>data State s a = State { runState :: s -> (a, s) }</code></pre></div>

548+<div class="sourceCode" id="cb90"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb90-1"></a>class Monad (State s) where

549+<a href="#cb90-2"></a> return x = State (\s -> (x, s))

550+<a href="#cb90-3"></a>

551+<a href="#cb90-4"></a> (>>=) :: State s a -> (a -> State s b) -> State s b

552+<a href="#cb90-5"></a> (State f) >>= g = State go

553+<a href="#cb90-6"></a> where

554+<a href="#cb90-7"></a> go s = runState (g a) s'

555+<a href="#cb90-8"></a> where

556+<a href="#cb90-9"></a> (a, s') = f s</code></pre></div>

557+</section>

558+<section class="slide level2">

559+

560+<h3 id="айдишники">Айдишники!</h3>

561+<div class="sourceCode" id="cb91"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb91-1"></a>getNewId :: State Int Int

562+<a href="#cb91-2"></a>getNewId = do

563+<a href="#cb91-3"></a> newId <- get

564+<a href="#cb91-4"></a> put (newId + 1)

565+<a href="#cb91-5"></a> return newId</code></pre></div>

566+– Это какой-то процедурный языке получается!

567+– Лучше!*

568+<div class="sourceCode" id="cb92"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb92-1"></a>createOrder :: Coffee -> State Int Order

569+<a href="#cb92-2"></a>createOrder coffee = do

570+<a href="#cb92-3"></a> newId <- getNewId

571+<a href="#cb92-4"></a> return (Order coffee newId)

572+<a href="#cb92-5"></a>

573+<a href="#cb92-6"></a>createOrders :: [Coffee] -> State Int [Order]

574+<a href="#cb92-7"></a>createOrders = mapM createOrder</code></pre></div>

575+</section>

576+<section id="еще-монады" class="slide level2">

577+<h2>Еще монады!</h2>

578+<div class="sourceCode" id="cb93"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb93-1"></a>class Monad [] where

579+<a href="#cb93-2"></a> return x = [x]

580+<a href="#cb93-3"></a>

581+<a href="#cb93-4"></a> (>>=) :: [a] -> (a -> [b]) -> [b]

582+<a href="#cb93-5"></a> [] >>= _ = []

583+<a href="#cb93-6"></a> (a : aa) >>= f = f a <> (a >>= f)</code></pre></div>

584+Контекст недетерменированности (нескольких вариантов)

585+<div class="sourceCode" id="cb94"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb94-1"></a>grid = do

586+<a href="#cb94-2"></a> x <- [1..5]

587+<a href="#cb94-3"></a> y <- [1..5]

588+<a href="#cb94-4"></a> return (x, y)

589+<a href="#cb94-5"></a>

590+<a href="#cb94-6"></a>-- [(1,1),(1,2),(1,3),(1,4),(1,5),(2,1),(2,2),(2,3),(2,4),(2,5),(3,1),(3,2),(3,3),(3,4),(3,5),(4,1),(4,2),(4,3),(4,4),(4,5),(5,1),(5,2),(5,3),(5,4),(5,5)]</code></pre></div>

591+</section>

592+<section class="slide level2">

593+

594+Тривиальная монада

595+<div class="sourceCode" id="cb95"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb95-1"></a>data Identity a = Identity { runIdentity :: a }

596+<a href="#cb95-2"></a>

597+<a href="#cb95-3"></a>class Monad Identity where

598+<a href="#cb95-4"></a> return x = Identity x

599+<a href="#cb95-5"></a>

600+<a href="#cb95-6"></a> (>>=) :: Identity a -> (a -> Identity b) -> Identity b

601+<a href="#cb95-7"></a> (Identity a) >>= f = Identity (f a)</code></pre></div>

602+</section>

603+<section class="slide level2">

604+

605+<div class="sourceCode" id="cb96"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb96-1"></a>class Applicative m => Monad m where

606+<a href="#cb96-2"></a> return :: a -> m a

607+<a href="#cb96-3"></a> (>>=) :: m a -> (a -> m b) -> m b</code></pre></div>

608+Монада – перегрузка композиции функций.

609+<div class="sourceCode" id="cb97"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb97-1"></a>class Functor m => Applicative m where

610+<a href="#cb97-2"></a> pure :: a -> m a

611+<a href="#cb97-3"></a> (<*>) :: m (a -> b) -> m a -> m b</code></pre></div>

612+Аппликативный функтор – перегрузка применения функций.

613+– Почему не <code>(a -> b) -> f a -> f b</code>.

614+– Это <code>fmap</code>. (И функции нескольких аргументов)

615+</section>

616+<section class="slide level2">

617+

618+<div class="sourceCode" id="cb98"><pre class="sourceCode haskell"><code class="sourceCode haskell"><a href="#cb98-1"></a>(a -> b) -> f a -> f b</code></pre></div>

619+<div class="sourceCode" id="cb99"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb99-1"></a>(a -> (b -> c)) -> f a -> f (b -> c)</code></pre></div>

620+<div class="sourceCode" id="cb100"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb100-1"></a>getMarkup :: Env Markup

621+<a href="#cb100-2"></a>getPrice :: Env Price

622+<a href="#cb100-3"></a>getPayment :: Markup -> Price -> Payment</code></pre></div>

623+<div class="sourceCode" id="cb101"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb101-1"></a>payment :: Env Payment

624+<a href="#cb101-2"></a>payment = fmap getPayment getMarkup <*> getPrice</code></pre></div>

625+<div class="sourceCode" id="cb102"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb102-1"></a>payment = fmap getPayment getMarkup <*> getPrice

626+<a href="#cb102-2"></a>-- ^-------------^

627+<a href="#cb102-3"></a>-- Env Markup -> Env (Price -> Payment)</code></pre></div>

628+<div class="sourceCode" id="cb103"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb103-1"></a>(<$>) = fmap</code></pre></div>

629+<div class="sourceCode" id="cb104"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb104-1"></a>payment = getPayment <$> getMarkup <*> getPrice</code></pre></div>

630+</section>

631+<section class="slide level2">

632+

633+<div class="sourceCode" id="cb105"><pre class="sourceCode haskell fragment"><code class="sourceCode haskell"><a href="#cb105-1"></a>(<*>) :: m (a -> b) -> m a -> m b

634+<a href="#cb105-2"></a>f <*> ma = ma >>= \a -> fmap (\f' -> f' a) f</code></pre></div>

635+</section></section>

164636 </div>

165637 </div>

166638

3.md+775−1

@@ -3,7 +3,26 @@ theme: superblack

33author: Ilya Kostyuchenko

44---

6−### Библиотека про математику

6+# Функциональное программирование

8+---

10+## Напоминалочка

11+

12+```{ .haskell }

13+class Functor f where

14+ fmap :: (a -> b) -> f a -> f b

15+```

16+

17+```{ .haskell .fragment }

18+class Functor f => Alternative f where

19+ (<|>) :: f a -> f a -> f a

20+ empty :: f a

21+```

22+

23+---

24+

25+## Библиотека про математику

726#### (на джаве)

827

928```{ .java .fragment }

@@ -62,6 +81,761 @@ static int add(int x, int y, Logger log) {

6281

6382---

6483

84+```{ .haskell }

85+add :: Int -> Int -> (Int, String)

86+add x y = (x + y, "add " + show x + show y)

87+```

88+

89+[Неудобно программировать]{ .fragment }

90+

91+```{ .haskell .fragment }

92+add :: Int -> Int -> Int

93+times :: Int -> Int -> Int

94+

95+add8AndDouble :: Int -> Int

96+add8AndDouble = times 2 . add 8

97+```

98+

99+---

100+

101+```{ .haskell }

102+add :: Int -> Int -> (Int, String)

103+times :: Int -> Int -> (Int, String)

104+```

105+

106+```{ .haskell .fragment }

107+add8AndDouble :: Int -> (Int, String)

108+add8AndDouble x = (y2, log1 <> log2)

109+ where

110+ (y1, log1) = add 8 x

111+ (y2, log2) = times 2 y1

112+```

113+

114+![](images/ohno.png){height=200px .fragment}

115+

116+```{ .haskell .fragment }

117+add8AndDouble :: Int -> Int

118+add8AndDouble = times 2 . add 8

119+```

120+

121+---

122+

123+```{ .haskell }

124+data WithLog a = WithLog a String

125+```

126+

127+```{ .haskell .fragment }

128+add :: Int -> Int -> WithLog Int

129+times :: Int -> Int -> WithLog Int

130+```

131+

132+```{ .haskell .fragment }

133+add8AndDouble :: Int -> WithLog Int

134+add8AndDouble = times 2 `magic` add 8

135+```

136+

137+```{ .haskell .fragment }

138+magic ::

139+ (Int -> WithLog Int) ->

140+ (Int -> WithLog Int) ->

141+ (Int -> WithLog Int)

142+```

143+

144+```{ .haskell .fragment }

145+magic f g x1 = WithLog x3 (log1 <> log2)

146+ where

147+ (WithLog x2 log1) = g x1

148+ (WithLog x3 log2) = f x2

149+```

150+

151+---

152+

153+```{ .haskell }

154+magic ::

155+ (Int -> WithLog Int) ->

156+ (Int -> WithLog Int) ->

157+ (Int -> WithLog Int)

158+```

159+

160+```{ .haskell .fragment }

161+(<=<) ::

162+ (Int -> WithLog Int) ->

163+ (Int -> WithLog Int) ->

164+ (Int -> WithLog Int)

165+```

166+

167+```{ .haskell .fragment }

168+add8AndDouble :: Int -> WithLog Int

169+add8AndDouble = times 2 <=< add 8

170+```

171+

172+---

173+

174+```{ .haskell }

175+factor :: Int -> WithLog [Int]

176+

177+sum :: [Int] -> WithLog Int

178+```

179+

180+```{ .haskell .fragment }

181+sumFactors :: Int -> WithLog [Int]

182+sumFactors = sum <=< factor -- Doesn't work :(

183+```

184+

185+```{ .haskell .fragment }

186+(<=<) ::

187+ (Int -> WithLog Int) ->

188+ (Int -> WithLog Int) ->

189+ (Int -> WithLog Int)

190+```

191+

192+```{ .haskell .fragment }

193+(<=<) ::

194+ (b -> WithLog c ) ->

195+ (a -> WithLog b ) ->

196+ (a -> WithLog c )

197+```

198+

199+```{ .haskell .fragment }

200+(.) ::

201+ (b -> c ) ->

202+ (a -> b ) ->

203+ (a -> c )

204+```

205+

206+---

207+

208+```{ .haskell }

209+getCoffee :: Order -> Maybe Coffee

210+payForCoffee :: Coffee -> Maybe Payment

211+```

212+

213+```{ .haskell .fragment }

214+buyCoffee :: Order -> Maybe Payment

215+buyCoffee = payForCoffee <=< getCoffee

216+```

217+

218+```{ .haskell .fragment }

219+getCoffee :: Order -> Either CoffeeError Coffee

220+payForCoffee :: Coffee -> Either CoffeeError Payment

221+```

222+

223+```{ .haskell .fragment }

224+buyCoffee :: Order -> Either CoffeeError Payment

225+buyCoffee = payForCoffee <=< getCoffee

226+```

227+

228+```{ .haskell .fragment }

229+(<=<) ::

230+ Composable m =>

231+ (b -> m c) ->

232+ (a -> m b) ->

233+ (a -> m c)

234+```

235+

236+---

237+

238+```{ .haskell }

239+class Applicative m => Monad m where

240+ (<=<) :: (b -> m c) -> (a -> m b) -> (a -> m c)

241+```

242+

243+```{ .haskell .fragment }

244+instance Monad Maybe where

245+ (<=<) f g x = case g x of

246+ Nothing -> Nothing

247+ Just x2 -> f x2

248+```

249+

250+```{ .haskell .fragment }

251+instance Monad (Either e) where

252+ (<=<) f g x = case g x of

253+ Left e -> Left e

254+ Right x2 -> f x2

255+```

256+

65257```{ .haskell .fragment }

258+instance Monad WithLog where

259+ (<=<) f g x = WithLog x3 (log1 <> log2)

260+ where

261+ (WithLog x2 log1) = g x1

262+ (WithLog x3 log2) = f x2

263+```

264+

265+---

266+

267+### Больше операторов!

268+

269+```{ .haskell .fragment }

270+(<=<) :: Monad m => (b -> m c) -> (a -> m b) -> (a -> m c)

271+```

272+```{ .haskell .fragment }

273+buyCoffee :: Order -> Maybe Payment

274+buyCoffee = payForCoffee <=< getCoffee

275+```

276+

277+```{ .haskell .fragment }

278+flip :: (a -> b -> c) -> (b -> a -> c)

279+flip f b a = f a b

280+```

281+

282+```{ .haskell .fragment }

283+(>=>) :: Monad m => (a -> m b) -> (b -> m c) -> (a -> m c)

284+(>=>) = flip (<=<)

285+```

286+

287+```{ .haskell .fragment }

288+buyCoffee = getCoffee >=> payForCoffee

289+```

290+

291+---

292+

293+### Маленькое отступление

294+

295+`f :: () -> a` эквивалентно `f :: a`

296+

297+[Потому что у `()` всего одно значение (`()`), а любая функция для одинаковых аргументов всегда возвращает одинаковые значения (потому что по-другому невозможно).]{ .fragment }

298+

299+---

300+

301+```{ .haskell }

302+(>=>) :: Monad m => (a -> m b) -> (b -> m c) -> (a -> m c)

303+```

304+

305+```{ .haskell .fragment }

306+(>>=) :: Monad m => m b -> (b -> m c) -> m c

307+```

308+

309+```{ .haskell .fragment }

310+buyCoffee :: Order -> Maybe Payment

311+buyCoffee order = getCoffee order >>= payForCoffee

312+```

313+

314+```{ .haskell .fragment }

315+maybeBuyCoffee :: Myabe Order -> Maybe Payment

316+maybeBuyCoffee order = order >>= buyCoffee

317+```

318+

319+```{ .haskell .fragment }

320+(>>=) :: Monad m => m b -> (b -> m c) -> m c

321+```

322+

323+```{ .haskell .fragment }

324+(>=>) :: Monad m => (a -> m b) -> (b -> m c) -> (a -> m c)

325+```

326+

327+```{ .haskell .fragment }

328+ (() -> m b) -> (b -> m c) -> (() -> m c)

329+```

330+```{ .haskell .fragment }

331+ m b -> (b -> m c) -> m c

332+```

333+

334+---

335+

336+```{ .haskell }

337+(>=>) :: Monad m => (a -> m b) -> (b -> m c) -> (a -> m c)

338+```

339+

340+```{ .haskell }

341+(>>=) :: Monad m => m b -> (b -> m c) -> m c

342+(>>=) mb f = ( (\() -> mb) >=> f ) ()

343+```

344+

345+```{ .haskell .fragment }

346+(>>=) mb f = ( (\() -> mb) >=> f ) ()

347+-- () -> m b |

348+-- b -> m c

349+--

350+-- ^-------------------^

351+-- () -> m c

352+```

353+

354+---

355+

356+### Время раскрыть ложь

357+

358+```{ .haskell }

359+class Applicative m => Monad m where

360+ (>>=) :: m a -> (a -> m b) -> m b

361+ return :: a -> m a

362+```

363+

364+```{ .haskell .fragment }

365+ -- Law:

366+ ma :: m a

367+ (ma >>= return) == ma

368+```

369+

370+```{ .haskell .fragment }

371+ -- Law:

372+ f :: a -> m b

373+ (f >=> return) == f

374+```

375+

376+[`return` -- нейтральный элемент по `>=>`]{.fragment}

377+

378+```{ .haskell .fragment }

379+ -- Law:

380+ x :: a

381+ f :: a -> m b

382+ (return x >>= f) == f x

383+```

384+

385+---

386+

387+```{ .haskell }

388+instance Monad Maybe where

389+ ma >>= f = case ma of

390+ Nothing -> Nothing

391+ Just a -> f a

392+

393+ return a = Just a

394+```

395+

396+```{ .haskell .fragment }

397+instance Monad (Either e) where

398+ ma >>= f = case ma of

399+ Left e -> Left e

400+ Right a -> f a

401+

402+ return a = Right a

403+```

404+

405+```{ .haskell .fragment }

406+instance Monad WithLog where

407+ (WithLog a log1) >>= f = WithLog b (log1 <> log2)

408+ where

409+ WithLog b log2 = f a

410+

411+ return a = WithLog a ""

412+```

413+

414+---

415+

416+## More Monads!

417+

418+```{ .haskell }

419+type Markup = Int

420+

421+getCoffee :: Markup -> Order -> Coffee

422+payForCoffee :: Markup -> Coffee -> Payment

423+

424+buyCoffee :: Markup -> Order -> Payment

425+buyCoffee markup = payForCoffee markup . getCoffee markup

426+```

427+

428+```{ .haskell .fragment }

429+data Reader r a = Reader

430+ { runReader :: r -> a

431+ }

432+```

433+

434+[`r` -- то, что у нас в "окружении".]{ .fragment }

435+

436+```{ .haskell .fragment }

437+getCoffee :: Order -> Reader Markup Coffee

438+payForCoffee :: Coffee -> Reader Markup Payment

439+```

440+

441+```{ .haskell .fragment }

442+payment :: Payment

443+payment = runReader (payForCoffee coffee) markup

444+```

66445

446+---

447+

448+```{ .haskell }

449+data Reader r a = Reader { runReader :: r -> a }

450+

451+getCoffee :: Order -> Reader Markup Coffee

452+payForCoffee :: Coffee -> Reader Markup Payment

453+```

454+

455+```{ .haskell .fragment }

456+buyCoffee :: Order -> Reader Markup Payment

457+buyCoffee = payForCoffee <=< getCoffee

458+```

459+

460+

461+```{ .haskell .fragment }

462+type PricingEnv = Reader Markup

463+```

464+

465+```{ .haskell .fragment }

466+getCoffee :: Order -> PricingEnv Coffee

467+payForCoffee :: Coffee -> PricingEnv Payment

468+buyCoffee :: Order -> PricingEnv Payment

469+buyCoffee = payForCoffee <=< getCoffee

470+```

471+

472+---

473+

474+```{ .haskell }

475+data Reader r a = Reader

476+ { runReader :: r -> a

477+ }

478+

479+instance Monad (Reader r) where

480+ return a = Reader (\_ -> a)

481+

482+ (Reader g) >>= f = Reader ( \r -> runReader (f (g r)) r )

483+```

484+

485+```{ .haskell .fragment}

486+ (>>=) :: Reader r a -> (a -> Reader r b) -> Reader r b

487+

488+ (Reader g) >>= f = Reader ( \r -> runReader (f (g r)) r )

489+-- ^---^

490+-- a

491+-- ^-------^

492+-- Reader r b

493+-- ^-----------------^

494+-- r -> b

495+```

496+

497+---

498+

499+```{ .haskell }

500+type Price = Int

501+getCoffeePrice :: Markup -> Coffee -> Price

502+getDiscount :: Markup -> Coffee -> Price

503+getPayment :: Markup -> Price -> Payment

504+

505+payForCoffee :: Markup -> Coffee -> Payment

506+payForCoffee markup coffee = getPayment markup amount

507+ where

508+ coffeePrice = getCoffeePrice markup coffee

509+ discount = getDiscount markup coffee

510+ amount = coffeePrice - discount

511+```

512+

513+```{ .haskell .fragment }

514+type PricingEnv = Reader Markup

515+

516+getCoffeePrice :: Coffee -> PricingEnv Price

517+getDiscount :: Coffee -> PricingEnv Price

518+getPayment :: Price -> PricingEnv Payment

519+

520+payForCoffee :: Coffee -> PricingEnv Payment

521+payForCoffee coffee =

522+ coffee >>= getCoffeePrice >>= \coffeePrice ->

523+ coffee >>= getDiscount >>= \discount ->

524+ getPayment (coffeePrice - discount)

525+```

526+

527+---

528+

529+## Do syntax

530+

531+```{ .haskell .fragment }

532+bar :: Reader r a

533+qux :: a -> Reader r b

534+

535+foo :: Reader r b

536+foo = bar >>= \a -> qux a

537+```

538+

539+```{ .haskell .fragment }

540+foo = do

541+ a <- bar

542+ qux a

543+```

544+

545+```{ .haskell .fragment }

546+foo = do

547+ a <- bar

548+ b <- qux a

549+ return b

550+```

551+

552+---

553+

554+```{ .haskell }

555+type PricingEnv = Reader Markup

556+

557+getCoffeePrice :: Coffee -> PricingEnv Price

558+getDiscount :: Coffee -> PricingEnv Price

559+getPayment :: Price -> PricingEnv Payment

560+

561+payForCoffee :: Coffee -> PricingEnv Payment

562+payForCoffee coffee =

563+ coffee >>= getCoffeePrice >>= \coffeePrice ->

564+ coffee >>= getDiscount >>= \discount ->

565+ getPayment (coffeePrice - discount)

566+```

567+

568+```{ .haskell .fragment }

569+payForCoffee :: Coffee -> PricingEnv Payment

570+payForCoffee coffee = do

571+ coffeePrice <- getCoffeePrice coffee

572+ discount <- getDiscount coffee

573+ getPayment (coffeePrice - discount)

574+```

575+

576+---

577+

578+## Let statement

579+

580+```{ .haskell }

581+payForCoffee :: Coffee -> PricingEnv Payment

582+payForCoffee coffee = do

583+ coffeePrice <- getCoffeePrice coffee

584+ discount <- getDiscount coffee

585+ getPayment (coffeePrice - discount)

586+```

587+

588+

589+```{ .haskell .fragment }

590+payForCoffee :: Coffee -> PricingEnv Payment

591+payForCoffee coffee = do

592+ coffeePrice <- getCoffeePrice coffee

593+ discount <- getDiscount coffee

594+ let amount = coffeePrice - discount

595+ getPayment amount

596+```

597+

598+---

599+

600+```{ .haskell }

601+type PricingEnv = Reader Markup

602+type Price = Int

603+

604+data Coffee = Coffee { getCoffeePrice :: Price }

605+

606+getCoffeePrice :: Coffee -> PricingEnv Price

607+```

608+

609+```{ .haskell .fragment }

610+data Reader r a = Reader { runReader :: r -> a}

611+```

612+

613+```{ .haskell .fragment }

614+ask :: Reader r r

615+ask = Reader (\r -> r)

616+```

617+

618+```{ .haskell .fragment }

619+getCoffeePrice :: Coffee -> PricingEnv Price

620+getCoffeePrice coffee = do

621+ markup <- ask

622+ let coffePrice = getCoffeePrice coffee

623+ return (coffee + markup)

624+```

625+

626+---

627+

628+```{ .haskell }

629+data Order = Order { orderCoffee :: Coffee, orderId :: Int }

630+```

631+

632+```{ .haskell .fragment }

633+createOrder :: Coffee -> Order

634+```

635+

636+[Откуда брать `orderId`?]{ .fragment }

637+

638+```{ .haskell .fragment }

639+createOrder :: Coffee -> Reader Int Order

640+createOrder coffee = do

641+ newId <- ask

642+ return (Order coffee newId)

643+```

644+

645+[🎉]{ .fragment }

646+

647+```{ .haskell .fragment }

648+createOrders :: [Coffee] -> Reader Int [Order]

649+```

650+

651+```{ .haskell .fragment }

652+mapM :: (Monad m) => (a -> m b) -> [a] -> m [b]

653+```

654+

655+```{ .haskell .fragment }

656+createOrders = mapM createOrder

657+```

658+

659+---

660+

661+```{ .haskell }

662+createOrders :: [Coffee] -> Reader Int [Order]

663+createOrders = mapM createOrder

664+```

665+

666+[Все `id` будут одинаковые.]{ .fragment }

667+

668+[`Reader` эквивалентно глобальной **константе**.]{ .fragment }

669+

670+[Айдишники -- скорее глобальная **переменная**.]{ .fragment }

671+

672+[-- Но у нас же нет переменных!]{ .fragment }

673+

674+[-- Да, нет!]{ .fragment }

675+

676+---

677+

678+## State!

679+

680+```{ .haskell .fragment }

681+data State s a = ... -- s -- само состояние

682+

683+get :: State s s

684+put :: s -> State s ()

685+```

686+

687+```{ .haskell .fragment }

688+data State s a = State { runState :: s -> (a, s) }

689+

690+get :: State s s

691+get = State (\s -> (s, s))

692+

693+put :: s -> State s ()

694+put s = State (\_ -> ((), s))

695+```

696+

697+---

698+

699+```{ .haskell }

700+data State s a = State { runState :: s -> (a, s) }

701+```

702+

703+```{ .haskell .fragment }

704+class Monad (State s) where

705+ return x = State (\s -> (x, s))

706+

707+ (>>=) :: State s a -> (a -> State s b) -> State s b

708+ (State f) >>= g = State go

709+ where

710+ go s = runState (g a) s'

711+ where

712+ (a, s') = f s

713+```

714+

715+---

716+

717+### Айдишники!

718+

719+```{ .haskell .fragment }

720+getNewId :: State Int Int

721+getNewId = do

722+ newId <- get

723+ put (newId + 1)

724+ return newId

725+```

726+

727+[-- Это какой-то процедурный языке получается!]{ .fragment }

728+

729+[-- Лучше!*]{ .fragment }

730+

731+```{ .haskell .fragment }

732+createOrder :: Coffee -> State Int Order

733+createOrder coffee = do

734+ newId <- getNewId

735+ return (Order coffee newId)

736+

737+createOrders :: [Coffee] -> State Int [Order]

738+createOrders = mapM createOrder

739+```

740+

741+---

742+

743+## Еще монады!

744+

745+```{ .haskell .fragment }

746+class Monad [] where

747+ return x = [x]

748+

749+ (>>=) :: [a] -> (a -> [b]) -> [b]

750+ [] >>= _ = []

751+ (a : aa) >>= f = f a <> (a >>= f)

752+```

753+

754+[Контекст недетерменированности (нескольких вариантов)]{ .fragment }

755+

756+```{ .haskell .fragment }

757+grid = do

758+ x <- [1..5]

759+ y <- [1..5]

760+ return (x, y)

761+

762+-- [(1,1),(1,2),(1,3),(1,4),(1,5),(2,1),(2,2),(2,3),(2,4),(2,5),(3,1),(3,2),(3,3),(3,4),(3,5),(4,1),(4,2),(4,3),(4,4),(4,5),(5,1),(5,2),(5,3),(5,4),(5,5)]

763+```

764+

765+---

766+

767+Тривиальная монада

768+

769+```{ .haskell .fragment }

770+data Identity a = Identity { runIdentity :: a }

771+

772+class Monad Identity where

773+ return x = Identity x

774+

775+ (>>=) :: Identity a -> (a -> Identity b) -> Identity b

776+ (Identity a) >>= f = Identity (f a)

777+```

778+

779+---

780+

781+```{ .haskell }

782+class Applicative m => Monad m where

783+ return :: a -> m a

784+ (>>=) :: m a -> (a -> m b) -> m b

785+```

786+

787+[Монада -- перегрузка композиции функций.]{.fragment }

788+

789+```{ .haskell .fragment }

790+class Functor m => Applicative m where

791+ pure :: a -> m a

792+ (<*>) :: m (a -> b) -> m a -> m b

793+```

794+

795+[Аппликативный функтор -- перегрузка применения функций.]{.fragment }

796+

797+[-- Почему не `(a -> b) -> f a -> f b`.]{.fragment }

798+

799+[-- Это `fmap`. (И функции нескольких аргументов)]{.fragment }

800+

801+---

802+

803+```{ .haskell }

804+(a -> b) -> f a -> f b

805+```

806+

807+```{ .haskell .fragment }

808+(a -> (b -> c)) -> f a -> f (b -> c)

809+```

810+

811+```{ .haskell .fragment }

812+getMarkup :: Env Markup

813+getPrice :: Env Price

814+getPayment :: Markup -> Price -> Payment

815+```

816+

817+```{ .haskell .fragment }

818+payment :: Env Payment

819+payment = fmap getPayment getMarkup <*> getPrice

820+```

821+

822+```{ .haskell .fragment }

823+payment = fmap getPayment getMarkup <*> getPrice

824+-- ^-------------^

825+-- Env Markup -> Env (Price -> Payment)

826+```

827+

828+```{ .haskell .fragment }

829+(<$>) = fmap

830+```

831+

832+```{ .haskell .fragment }

833+payment = getPayment <$> getMarkup <*> getPrice

834+```

835+

836+---

837+

838+```{ .haskell .fragment }

839+(<*>) :: m (a -> b) -> m a -> m b

840+f <*> ma = ma >>= \a -> fmap (\f' -> f' a) f

67841```

README.md+11−4

@@ -1,4 +1,4 @@

1−## Lecures

1+## Lectures

33- Lecture 1 [[md](https://github.com/ikoHSE/sc-lectures/blob/master/1.md)] [[web](https://ikohse.github.io/sc-lectures/1.html)] [[Seminar](https://github.com/ikoHSE/sc-task-1)]

44 - [Functions](http://learnyouahaskell.com/starting-out#babys-first-functions)

@@ -18,12 +18,19 @@

1818 - [Typeclass instances](http://learnyouahaskell.com/making-our-own-types-and-typeclasses#typeclasses-102)

1919 - [Case](http://learnyouahaskell.com/syntax-in-functions#case-expressions)

2020 - [Polymorphic typeclass instances](http://learnyouahaskell.com/making-our-own-types-and-typeclasses#typeclasses-102)

21− - [`Monoid` typeclass](https://hackage.haskell.org/package/base-4.12.0.0/docs/Data-Monoid.html#t:Monoid)

22− - [`fold`](https://hackage.haskell.org/package/base-4.12.0.0/docs/Data-Foldable.html#v:fold)

21+ - [`Monoid` typeclass](http://learnyouahaskell.com/functors-applicative-functors-and-monoids#monoids)

22+ - [`fold`](http://learnyouahaskell.com/higher-order-functions#folds)

2323 - [Deriving](http://learnyouahaskell.com/making-our-own-types-and-typeclasses#derived-instances)

2424 - [Type synonyms](http://learnyouahaskell.com/making-our-own-types-and-typeclasses#type-synonyms)

2525 - Error handling

2626 - [`Maybe`](https://hackage.haskell.org/package/base-4.12.0.0/docs/Data-Maybe.html#t:Maybe)

2727 - [`Either`](https://hackage.haskell.org/package/base-4.12.0.0/docs/Data-Either.html#t:Either)

28− - [`Functor`](https://hackage.haskell.org/package/base-4.12.0.0/docs/Data-Functor.html#t:Functor)

28+ - [`Functor`](http://learnyouahaskell.com/functors-applicative-functors-and-monoids#functors-redux)

2929 - [`Alternative`](https://hackage.haskell.org/package/base-4.12.0.0/docs/Control-Applicative.html#t:Alternative)

30+- Lecture 2 [[md](https://github.com/ikoHSE/sc-lectures/blob/master/3.md)] [[web](https://ikohse.github.io/sc-lectures/3.html)] [[Seminar](https://github.com/ikoHSE/sc-task-3)]

31+ - [`Monad`](http://www.learnyouahaskell.com/a-fistful-of-monads)

32+ - [`Reader`](http://learnyouahaskell.com/for-a-few-monads-more#reader)

33+ - [`do` syntax](https://en.wikibooks.org/wiki/Haskell/do_notation#Translating_the_bind_operator)

34+ - [`mapM`](https://hackage.haskell.org/package/base-4.12.0.0/docs/Control-Monad.html#v:mapM)

35+ - [`State`](https://wiki.haskell.org/State_Monad)

36+ - [`Applicative`](http://learnyouahaskell.com/functors-applicative-functors-and-monoids#applicative-functors)

build.sh+1−1

@@ -5,6 +5,6 @@ do

55 base=$(basename $file .md)

66 if [ $base != "README" ]

77 then

8− pandoc -i $file -t revealjs -s --highlight-style=breezeDark --include-in-header=style.html >"$base.html"

8+ pandoc -i $file -t revealjs -s --highlight-style=breezeDark --include-in-header=style.html --highlight-style=highlight.theme >"$base.html"

99 fi

1010done

highlight.themenew file+225

@@ -0,0 +1,225 @@

1+{

2+ "text-color": "#ffffff",

3+ "background-color": "#000000",

4+ "line-number-color": "#7a7c7d",

5+ "line-number-background-color": "#232629",

6+ "text-styles": {

7+ "Other": {

8+ "text-color": "#86e9b0",

9+ "background-color": null,

10+ "bold": false,

11+ "italic": false,

12+ "underline": false

13+ },

14+ "Attribute": {

15+ "text-color": "#94cbf0",

16+ "background-color": null,

17+ "bold": false,

18+ "italic": false,

19+ "underline": false

20+ },

21+ "SpecialString": {

22+ "text-color": "#ff909b",

23+ "background-color": null,

24+ "bold": false,

25+ "italic": false,

26+ "underline": false

27+ },

28+ "Annotation": {

29+ "text-color": "#86d5a4",

30+ "background-color": null,

31+ "bold": false,

32+ "italic": false,

33+ "underline": false

34+ },

35+ "RegionMarker": {

36+ "text-color": "#83c7f4",

37+ "background-color": "#153042",

38+ "bold": false,

39+ "italic": false,

40+ "underline": false

41+ },

42+ "Function": {

43+ "text-color": "#d487f4",

44+ "background-color": null,

45+ "bold": false,

46+ "italic": false,

47+ "underline": false

48+ },

49+ "String": {

50+ "text-color": "#ff9f9f",

51+ "background-color": null,

52+ "bold": false,

53+ "italic": false,

54+ "underline": false

55+ },

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93+ "background-color": "#4d1f24",

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121+ "background-color": null,

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127+ "text-color": "#f6b176",

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139+ },

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141+ "text-color": "#eca2a9",

142+ "background-color": null,

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144+ "italic": false,

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146+ },

147+ "Documentation": {

148+ "text-color": "#a43340",

149+ "background-color": null,

150+ "bold": false,

151+ "italic": false,

152+ "underline": false

153+ },

154+ "Import": {

155+ "text-color": "#76e8a6",

156+ "background-color": null,

157+ "bold": false,

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177+ "background-color": null,

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183+ "text-color": "#a1a6a8",

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190+ "text-color": "#b6c8c9",

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194+ "underline": false

195+ },

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198+ "background-color": null,

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200+ "italic": false,

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202+ },

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204+ "text-color": "#80ccf4",

205+ "background-color": null,

206+ "bold": false,

207+ "italic": false,

208+ "underline": false

209+ },

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211+ "text-color": "#f6b77f",

212+ "background-color": null,

213+ "bold": false,

214+ "italic": false,

215+ "underline": false

216+ },

217+ "Keyword": {

218+ "text-color": "#ebebc9",

219+ "background-color": null,

220+ "bold": true,

221+ "italic": false,

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223+ }

224+ }

225+}

reveal.js/css/theme/source/superblack.scss+2−2

@@ -56,10 +56,10 @@ section.has-light-background {

5656}

5757

5858.reveal code {

59− background-color: #333;

59+ background-color: rgb(31, 31, 31);

6060 border-radius: 13px;

6161 padding: 0px 4px 0px 4px;

6262 border-width: 2px;

6363 border-style: solid;

64− border-color: #777;

64+ border-color: rgb(107, 107, 107);

6565}

reveal.js/css/theme/superblack.css+2−2

@@ -277,9 +277,9 @@ body {

277277 background-color: #222; }

278278

279279.reveal code {

280− background-color: #333;

280+ background-color: #1f1f1f;

281281 border-radius: 13px;

282282 padding: 0px 4px 0px 4px;

283283 border-width: 2px;

284284 border-style: solid;

285− border-color: #777; }

285+ border-color: #6b6b6b; }