Sample run of chapter's interpreter examples
elem(s: String): Element
// In file composition-and-inheritance/LayoutElement.scala val column1 = elem("hello") above elem("***") val column2 = elem("***") above elem("world") column1 beside column2
hello *** *** world
abstract class Element: def contents: Vector[String]
abstract class Element ...
scala> new Element 1 |new Element | ^^^^^^^ | Element is abstract; it cannot be instantiated
// In file composition-and-inheritance/Ex9.scala abstract class Element: def contents: Vector[String] def height: Int = contents.length def width: Int = if height == 0 then 0 else contents(0).length
def width(): Int
def width: Int
// In file composition-and-inheritance/Ex2.scala abstract class Element: def contents: Vector[String] val height = contents.length val width = if height == 0 then 0 else contents(0).length
// In file composition-and-inheritance/Ex2.scala Array(1, 2, 3).toString "abc".length
// In file composition-and-inheritance/Ex2.scala "hello".length // no () because no side-effect println() // better to not drop the ()
// In file composition-and-inheritance/Ex10.scala class VectorElement(conts: Vector[String]) extends Element: def contents: Vector[String] = conts
... extends Element ...
val ve = VectorElement(Vector("hello", "world")) ve.width // 5
// In file composition-and-inheritance/Ex2.scala val e: Element = VectorElement(Vector("hello"))
// In file composition-and-inheritance/Ex3.scala class VectorElement(conts: Vector[String]) extends Element: val contents: Vector[String] = conts
// This is Java class CompilesFine { private int f = 0; public int f() { return 1; } }
// In file composition-and-inheritance/Ex4.scala.err class WontCompile: private var f = 0 // Won't compile, because a field def f = 1 // and method have the same name
// In file composition-and-inheritance/Ex9.scala // Extends Element shown in Listing 10.2 class VectorElement( val contents: Vector[String] ) extends Element
class VectorElement(x123: Vector[String]) extends Element: val contents: Vector[String] = x123
// In file composition-and-inheritance/Ex8.scala class Cat: val dangerous = false class Tiger( override val dangerous: Boolean, private var age: Int ) extends Cat
// In file composition-and-inheritance/Ex8.scala class Tiger(param1: Boolean, param2: Int) extends Cat: override val dangerous = param1 private var age = param2
// In file composition-and-inheritance/Ex9.scala // Extends VectorElement shown in Listing 10.5 class LineElement(s: String) extends VectorElement(Vector(s)): override def width = s.length override def height = 1
... extends VectorElement(Vector(s)) ...
$ scalac LineElement.scala -- [E037] Declaration Error: LineElement.scala:3:15 -- 3 | override def hight = 1 | ^ | method hight overrides nothing
def hidden(): Boolean
-- Error: Circle.scala:3:6 --------------------------- 3 | def hidden(): Boolean = | ^ | error overriding method hidden in class Shape | of type (): Boolean; method hidden of type | (): Boolean needs `override` modifier
// In file composition-and-inheritance/Ex9.scala // Extends Element shown in Listing 10.2 class UniformElement( ch: Char, override val width: Int, override val height: Int ) extends Element: private val line = ch.toString * width def contents = Vector.fill(height)(line)
// In file composition-and-inheritance/Ex9.scala val e1: Element = VectorElement(Vector("hello", "world")) val ve: VectorElement = LineElement("hello") val e2: Element = ve val e3: Element = UniformElement('x', 2, 3)
abstract class Element: def demo = "Element's implementation invoked" class VectorElement extends Element: override def demo = "VectorElement's implementation invoked" class LineElement extends VectorElement: override def demo = "LineElement's implementation invoked" // UniformElement inherits Element's demo class UniformElement extends Element
def invokeDemo(e: Element) = e.demo
invokeDemo(new VectorElement) // VectorElement's implementation invoked
invokeDemo(new LineElement) // LineElement's implementation invoked
invokeDemo(new UniformElement) // Element's implementation invoked
class VectorElement extends Element: final override def demo = "VectorElement's implementation invoked"
-- Error: LineElement.scala:2:15 ---------------------- 2 | override def demo = | ^ |error overriding method demo in class VectorElement | of type => String; method demo of type => String | cannot override final member method demo in class | VectorElement
final class VectorElement extends Element: override def demo = "VectorElement's implementation invoked"
-- [E093] Syntax Error: LineElement.scala:1:6 --------- 1 |class LineElement extends VectorElement: | ^ | class LineElement cannot extend final class | VectorElement
// In file composition-and-inheritance/Ex10.scala class LineElement(s: String) extends Element: val contents = Vector(s) override def width = s.length override def height = 1
// In file composition-and-inheritance/Ex10.scala def above(that: Element): Element = VectorElement(this.contents ++ that.contents)
// In file composition-and-inheritance/Ex10.scala def beside(that: Element): Element = val newContents = new Array[String](this.contents.length) for i <- 0 until this.contents.length do newContents(i) = this.contents(i) + that.contents(i) VectorElement(newContents.toVector)
// In file composition-and-inheritance/Ex10.scala VectorElement( for (line1, line2) <- this.contents.zip(that.contents) yield line1 + line2)
// In file composition-and-inheritance/Ex10.scala Vector(1, 2, 3).zip(Vector("a", "b"))
// In file composition-and-inheritance/Ex10.scala Vector((1, "a"), (2, "b"))
// In file composition-and-inheritance/Ex10.scala override def toString = contents.mkString("\n")
// In file composition-and-inheritance/Ex11.scala abstract class Element: def contents: Vector[String] def width: Int = if height == 0 then 0 else contents(0).length def height: Int = contents.length def above(that: Element): Element = VectorElement(this.contents ++ that.contents) def beside(that: Element): Element = VectorElement( for (line1, line2) <- this.contents.zip(that.contents) yield line1 + line2 ) override def toString = contents.mkString("\n") end Element
// In file composition-and-inheritance/Ex12.scala object Element: def elem(contents: Vector[String]): Element = VectorElement(contents) def elem(chr: Char, width: Int, height: Int): Element = UniformElement(chr, width, height) def elem(line: String): Element = LineElement(line)
// In file composition-and-inheritance/Ex12.scala import Element.elem abstract class Element: def contents: Vector[String] def width: Int = if height == 0 then 0 else contents(0).length def height: Int = contents.length def above(that: Element): Element = elem(this.contents ++ that.contents) def beside(that: Element): Element = elem( for (line1, line2) <- this.contents.zip(that.contents) yield line1 + line2 ) override def toString = contents.mkString("\n") end Element
// In file composition-and-inheritance/LayoutElement.scala object Element: private class VectorElement( val contents: Vector[String] ) extends Element private class LineElement(s: String) extends Element: val contents = Vector(s) override def width = s.length override def height = 1 private class UniformElement( ch: Char, override val width: Int, override val height: Int ) extends Element: private val line = ch.toString * width def contents = Vector.fill(height)(line) def elem(contents: Vector[String]): Element = VectorElement(contents) def elem(chr: Char, width: Int, height: Int): Element = UniformElement(chr, width, height) def elem(line: String): Element = LineElement(line) end Element
elem(Vector("hello")) above elem(Vector("world!"))
elem(Vector("one", "two")) beside elem(Vector("one"))
// In file composition-and-inheritance/LayoutElement.scala import Element.elem abstract class Element: def contents: Vector[String] def width: Int = if height == 0 then 0 else contents(0).length def height: Int = contents.length def above(that: Element): Element = val this1 = this.widen(that.width) val that1 = that.widen(this.width) elem(this1.contents ++ that1.contents) def beside(that: Element): Element = val this1 = this.heighten(that.height) val that1 = that.heighten(this.height) elem( for (line1, line2) <- this1.contents.zip(that1.contents) yield line1 + line2 ) def widen(w: Int): Element = if w <= width then this else val left = elem(' ', (w - width) / 2, height) val right = elem(' ', w - width - left.width, height) left beside this beside right def heighten(h: Int): Element = if h <= height then this else val top = elem(' ', width, (h - height) / 2) val bot = elem(' ', width, h - height - top.height) top above this above bot override def toString = contents.mkString("\n") end Element
// In file composition-and-inheritance/Spiral.scala import Element.elem object Spiral: val space = elem(" ") val corner = elem("+") def spiral(nEdges: Int, direction: Int): Element = if nEdges == 1 then elem("+") else val sp = spiral(nEdges - 1, (direction + 3) % 4) def verticalBar = elem('|', 1, sp.height) def horizontalBar = elem('-', sp.width, 1) if direction == 0 then (corner beside horizontalBar) above (sp beside space) else if direction == 1 then (sp above space) beside (corner above verticalBar) else if direction == 2 then (space beside sp) above (horizontalBar beside corner) else (verticalBar above corner) beside (space above sp) def main(args: Array[String]) = val nSides = args(0).toInt println(spiral(nSides, 0)) end Spiral
$ scala Spiral 6 $ scala Spiral 11 $ scala Spiral 17 +----- +---------- +---------------- | | | | +-+ | +------+ | +------------+ | + | | | | | | | | | | | +--+ | | | +--------+ | +---+ | | | | | | | | | | | | ++ | | | | | +----+ | | | | | | | | | | | | | | +----+ | | | | | ++ | | | | | | | | | | | | | +--------+ | | | +--+ | | | | | | | | | | | +------+ | | | | | | | +----------+ | | | +--------------+
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