Added the current version of koans in a new format

Author: svtk

.gitignore

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+.idea

Builders/Builders how it works/src/Task.kt

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+import Answer.*
+
+enum class Answer { a, b, c }
+
+val answers = mapOf<Int, Answer?>(
+        1 to c, 2 to b, 3 to b, 4 to c
+)

Builders/Builders how it works/task-info.yaml

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+type: edu
+files:
+- name: src/Task.kt
+  visible: true
+  placeholders:
+  - offset: 91
+    length: 30
+    placeholder_text: 1 to null, 2 to null, 3 to null, 4 to null
+- name: test/tests.kt
+  visible: false

Builders/Builders how it works/task-remote-info.yaml

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+id: 234760
+update_date: Thu, 15 Feb 2018 10:40:54 UTC

Builders/Builders how it works/task.html

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+<h2>Builders: how it works</h2>
+<p>Look at the questions below and give your answers</p>
+<p><strong>1. In the Kotlin code</strong></p><pre><code data-lang="text/x-kotlin">tr {
+    td {
+        text(&quot;Product&quot;)
+    }
+    td {
+        text(&quot;Popularity&quot;)
+    }
+}
+</code></pre>
+<p><strong>'td' is:</strong></p>
+<p>a. special built-in syntactic construct</p>
+<p>b. function declaration</p>
+<p>c. function invocation</p>
+<hr/>
+<p><strong>2. In the Kotlin code</strong></p><pre><code data-lang="text/x-kotlin">tr (color = &quot;yellow&quot;) {
+    td {
+        text(&quot;Product&quot;)
+    }
+    td {
+        text(&quot;Popularity&quot;)
+    }
+}
+</code></pre>
+<p><strong>'color' is:</strong></p>
+<p>a. new variable declaration</p>
+<p>b. argument name</p>
+<p>c. argument value</p>
+<hr/>
+<p><strong>3. The block</strong></p><pre><code data-lang="text/x-kotlin">{
+    text(&quot;Product&quot;)
+}
+</code></pre>
+<p><strong>from the previous question is:</strong></p>
+<p>a. block inside built-in syntax construction <code>td</code></p>
+<p>b. function literal (or "lambda")</p>
+<p>c. something mysterious</p>
+<hr/>
+<p><strong>4. For the code</strong></p><pre><code data-lang="text/x-kotlin">tr (color = &quot;yellow&quot;) {
+    this.td {
+        text(&quot;Product&quot;)
+    }
+    td {
+        text(&quot;Popularity&quot;)
+    }
+}
+</code></pre>
+<p><strong>which of the following is true:</strong></p>
+<p>a. this code doesn't compile</p>
+<p>b. <code>this</code> refers to an instance of an outer class</p>
+<p>c. <code>this</code> refers to a receiver parameter TR of the function literal:</p><pre><code data-lang="text/x-kotlin">tr (color = &quot;yellow&quot;) { TR.(): Unit -&gt;
+      this.td {
+          text(&quot;Product&quot;)
+      }
+}
+</code></pre>

Builders/Builders how it works/test/tests.kt

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+import org.junit.Test
+import org.junit.Assert
+import Answer.*
+
+class TestBuildersHowItWorks {
+    @Test fun testBuildersQuiz() {
+        if (answers.values.toSet() == setOf(null)) {
+            Assert.fail("Please specify your answers!")
+        }
+        val correctAnswers = mapOf(22 - 20 to b, 1 + 3 to c, 11 - 8 to b, 79 - 78 to c)
+        if (correctAnswers != answers) {
+            val incorrect = (1..4).filter { answers[it] != correctAnswers[it] }
+            Assert.fail("Your answers are incorrect! $incorrect")
+        }
+    }
+}

Builders/Function literals with receiver/src/Task.kt

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+fun task(): List<Boolean> {
+    val isEven: Int.() -> Boolean = { this % 2 == 0 }
+    val isOdd: Int.() -> Boolean = { this % 2 != 0 }
+
+    return listOf(42.isOdd(), 239.isOdd(), 294823098.isEven())
+}

Builders/Function literals with receiver/task-info.yaml

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+type: edu
+files:
+- name: src/Task.kt
+  visible: true
+  placeholders:
+  - offset: 66
+    length: 13
+    placeholder_text: TODO()
+  - offset: 119
+    length: 13
+    placeholder_text: TODO()
+- name: test/tests.kt
+  visible: false

Builders/Function literals with receiver/task-remote-info.yaml

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+id: 234756
+update_date: Thu, 15 Feb 2018 10:40:49 UTC

Builders/Function literals with receiver/task.html

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+<h2>Extension function literals</h2>
+<p>Read about <a href="https://kotlinlang.org/docs/reference/lambdas.html#function-literals-with-receiver">function literals with receiver</a>.</p>
+<p>You can declare <code>isEven</code> and <code>isOdd</code> as values, that can be called as extension functions. Complete the declarations below.</p>

Builders/Function literals with receiver/test/tests.kt

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+import org.junit.Assert
+import org.junit.Test
+import koans.util.inEquals
+
+class TestExtensionFunctionLiterals {
+    @Test fun testIsOddAndIsEven() {
+        Assert.assertEquals("The functions 'isOdd' and 'isEven' should be implemented correctly".inEquals(),
+                listOf(false, true, true), task())
+
+    }
+}

Builders/Html builders/src/Task.kt

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+fun renderProductTable(): String {
+    return html {
+        table {
+            tr (color = getTitleColor()){
+                td {
+                    text("Product")
+                }
+                td {
+                    text("Price")
+                }
+                td {
+                    text("Popularity")
+                }
+            }
+            val products = getProducts()
+            for ((index, product) in products.withIndex()) {
+                tr {
+                    td (color = getCellColor(index, 0)) {
+                        text(product.description)
+                    }
+                    td (color = getCellColor(index, 1)) {
+                        text(product.price)
+                    }
+                    td (color = getCellColor(index, 2)) {
+                        text(product.popularity)
+                    }
+                }
+            }
+        }
+    }.toString()
+}
+
+fun getTitleColor() = "#b9c9fe"
+fun getCellColor(index: Int, row: Int) = if ((index + row) %2 == 0) "#dce4ff" else "#eff2ff"

Builders/Html builders/src/data.kt

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+data class Product(val description: String, val price: Double, val popularity: Int)
+
+val cactus = Product("cactus", 11.2, 13)
+val cake = Product("cake", 3.2, 111)
+val camera = Product("camera", 134.5, 2)
+val car = Product("car", 30000.0, 0)
+val carrot = Product("carrot", 1.34, 5)
+val cellPhone = Product("cell phone", 129.9, 99)
+val chimney = Product("chimney", 190.0, 2)
+val certificate = Product("certificate", 99.9, 1)
+val cigar = Product("cigar", 8.0, 51)
+val coffee = Product("coffee", 8.0, 67)
+val coffeeMaker = Product("coffee maker", 201.2, 1)
+val cola = Product("cola", 4.0, 67)
+val cranberry = Product("cranberry", 4.1, 39)
+val crocs = Product("crocs", 18.7, 10)
+val crocodile = Product("crocodile", 20000.2, 1)
+val cushion = Product("cushion", 131.0, 0)
+
+fun getProducts() = listOf(cactus, cake, camera, car, carrot, cellPhone, chimney, certificate, cigar, coffee, coffeeMaker,
+        cola, cranberry, crocs, crocodile, cushion)

Builders/Html builders/src/demo.kt

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+import javax.swing.JFrame
+import javax.swing.JLabel
+import javax.swing.JScrollPane
+import javax.swing.SwingConstants.CENTER
+
+fun main(args: Array<String>) {
+    with (JFrame("Product popularity")) {
+        setSize(600, 600)
+        defaultCloseOperation = JFrame.EXIT_ON_CLOSE
+        add(JScrollPane(JLabel(renderProductTable(), CENTER)))
+        isVisible = true
+    }
+}

Builders/Html builders/src/html.kt

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+import java.util.ArrayList
+
+open class Tag(val name: String) {
+    val children: MutableList<Tag> = ArrayList()
+    val attributes: MutableList<Attribute> = ArrayList()
+
+    override fun toString(): String {
+        return "<$name" +
+            (if (attributes.isEmpty()) "" else attributes.joinToString(separator = "", prefix = " ")) + ">" +
+            (if (children.isEmpty()) "" else children.joinToString(separator = "")) +
+            "</$name>"
+    }
+}
+
+class Attribute(val name : String, val value : String) {
+    override fun toString() = """$name="$value" """
+}
+
+fun <T: Tag> T.set(name: String, value: String?): T {
+    if (value != null) {
+        attributes.add(Attribute(name, value))
+    }
+    return this
+}
+
+fun <T: Tag> Tag.doInit(tag: T, init: T.() -> Unit): T {
+    tag.init()
+    children.add(tag)
+    return tag
+}
+
+class Html: Tag("html")
+class Table: Tag("table")
+class Center: Tag("center")
+class TR: Tag("tr")
+class TD: Tag("td")
+class Text(val text: String): Tag("b") {
+    override fun toString() = text
+}
+
+fun html(init: Html.() -> Unit): Html = Html().apply(init)
+
+fun Html.table(init : Table.() -> Unit) = doInit(Table(), init)
+fun Html.center(init : Center.() -> Unit) = doInit(Center(), init)
+
+fun Table.tr(color: String? = null, init : TR.() -> Unit) = doInit(TR(), init).set("bgcolor", color)
+
+fun TR.td(color: String? = null, align : String = "left", init : TD.() -> Unit) = doInit(TD(), init).set("align", align).set("bgcolor", color)
+
+fun Tag.text(s : Any?) = doInit(Text(s.toString()), {})
+

Builders/Html builders/task-info.yaml

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+type: edu
+files:
+- name: src/html.kt
+  visible: true
+- name: src/Task.kt
+  visible: true
+  placeholders:
+  - offset: 84
+    length: 25
+    placeholder_text: /* TODO */
+  - offset: 404
+    length: 484
+    placeholder_text: TODO()
+- name: src/data.kt
+  visible: true
+- name: src/demo.kt
+  visible: true
+- name: test/tests.kt
+  visible: false

Builders/Html builders/task-remote-info.yaml

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+id: 234759
+update_date: Thu, 15 Feb 2018 10:40:52 UTC

Builders/Html builders/task.html

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+<h2>Html builder</h2>
+<p><em>1.</em> Fill the table with the proper values from the product list. The products are declared in <code>data.kt</code>.</p>
+<p><em>2.</em> Color the table like a chess board (using getTitleColor() and getCellColor() functions above). Pass a color as an argument to the functions <code>tr</code>, <code>td</code>.</p>
+<p>Open the file <code>demo.kt</code> and run the main function there to see the rendered table.</p>

Builders/Html builders/test/tests.kt

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+import org.junit.Assert
+import org.junit.Test
+
+class TestHtmlBuilders {
+    @Test fun productTableIsFilled() {
+        val result = renderProductTable()
+        Assert.assertTrue("Product table should contain the corresponding data", result.contains("cactus"))
+    }
+
+    @Test fun productTableIsColored() {
+        val result = renderProductTable()
+        Assert.assertTrue("Product table should be colored", result.contains("bgcolor"))
+    }
+}

Builders/String and map builders/src/Task.kt

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+import java.util.HashMap
+
+fun <K, V> buildMap(build: HashMap<K, V>.() -> Unit): Map<K, V> {
+    val map = HashMap<K, V>()
+    map.build()
+    return map
+}
+
+fun usage(): Map<Int, String> {
+    return buildMap {
+        put(0, "0")
+        for (i in 1..10) {
+            put(i, "$i")
+        }
+    }
+}

Builders/String and map builders/task-info.yaml

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+type: edu
+files:
+- name: src/Task.kt
+  visible: true
+  placeholders:
+  - offset: 26
+    length: 128
+    placeholder_text: /* TODO */
+- name: test/tests.kt
+  visible: false

Builders/String and map builders/task-remote-info.yaml

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+id: 234757
+update_date: Thu, 15 Feb 2018 10:40:50 UTC

Builders/String and map builders/task.html

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+<h2>String and map builders</h2>
+<p>Extension function literals are very useful for creating builders, e.g.:</p><pre><code data-lang="text/x-kotlin">fun buildString(build: StringBuilder.() -&gt; Unit): String {
+    val stringBuilder = StringBuilder()
+    stringBuilder.build()
+    return stringBuilder.toString()
+}
+
+val s = buildString {
+    this.append(&quot;Numbers: &quot;)
+    for (i in 1..3) {
+        // &#39;this&#39; can be omitted
+        append(i)
+    }
+}
+
+s == &quot;Numbers: 123&quot;
+</code></pre>
+<p>Add and implement the function 'buildMap' with one parameter (of type extension function) creating a new HashMap, building it and returning it as a result. The usage of this function is shown below.</p>

Builders/String and map builders/test/tests.kt

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+import org.junit.Assert
+import org.junit.Test
+import koans.util.inEquals
+
+class TestStringAndMapBuilders {
+    @Test fun testBuildMap() {
+        val map: Map<Int, String> = buildMap {
+            put(0, "0")
+            for (i in 1..10) {
+                put(i, "$i")
+            }
+        }
+        val expected = hashMapOf<Int, String>()
+        for (i in 0..10) {
+            expected[i] = "$i"
+        }
+        Assert.assertEquals("Map should be filled with the right values".inEquals(), expected, map)
+    }
+}