Programs that write other programs 1

Exercise 1. Write a Kotlin program that outputs to the terminal a Kotlin program that prints “Hello, world!” to the terminal.

Solution.

fun main(args: Array<String>) {
    println("""
        |fun main(args: Array<String>) {
        |    println("Hello, world!")
        |}
        """.trimMargin()
    )
}

Programs that write other programs 2

Exercise 2. Write a Kotlin program that writes to the terminal the content of an HTML file containing an SVG tag for drawing a 200x100 red rectangle with black outline with stroke-width equal to 3 in the upper left corner of a 640x360 area.

Solution:

fun main(args: Array<String>) {
    println("""
    |<html><head></head><body>
    |<svg width="640" height="360">
    |<rect x="0" y="0" width="200" height="100" stroke="black" stroke-width="3" fill="red" />
    |</svg>
    |</body>
    |</html>
    """.trimMargin())
}

Programs that write other programs 3

Exercise 3. Write a Kotlin program that outputs to the terminal the content of an HTML file containing an SVG tag for drawing 10 circles, each of random radius and center, and each filled with a random color. Each circle should have a black outline with stroke-width equal to 3.

Solution:

fun main(args: Array<String>) {
    val randGen = java.util.Random()
    val colors = arrayOf(
        "burlywood", "coral", "cyan", "darkgray", "lightgreen",
        "plum", "turquoise", "orange", "skyblue", "red")
    val WIDTH = 640
    val HEIGHT = 360
    val header = """
        |<html><head></head><body>
        |<svg width="$WIDTH" height="$HEIGHT">
        """.trimMargin()
    val footer = """
        |</svg>
        |</body>
        |</html>
        """.trimMargin()
    fun randomCircle() {
        val cx = randGen.nextInt(WIDTH)
        val cy = randGen.nextInt(HEIGHT)
        val r = randGen.nextInt(30) + 10
        val color = colors[randGen.nextInt(colors.size)]
        println("""
        |<circle cx="$cx" cy="$cy" r="$r" stroke="black" stroke-width="3" fill="$color" />
        """.trimMargin())
    }
    println(header)
    repeat(10) { randomCircle() }
    println(footer)
}

Programs that write other programs

San Skulrattanakulchai

October 19, 2018

Programs that write other programs 1

Programs that write other programs 2

Programs that write other programs 3