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package examples
import scala.xml._
object fors {
val e = Node.NoAttributes
class Person(_name: String, _age: Int) {
val name = _name
val age = _age
}
def printOlderThan20(xs: Seq[Person]): Iterator[String] =
printOlderThan20(xs.elements)
def printOlderThan20(xs: Iterator[Person]): Iterator[String] =
for (val p <- xs; p.age > 20) yield p.name
val persons = List(
new Person("John", 40),
new Person("Richard", 68)
)
def divisors(n: Int): List[Int] =
for (val i <- List.range(1, n+1); n % i == 0) yield i
def isPrime(n: Int) = divisors(n).length == 2
def findNums(n: Int): Iterator[Pair[Int, Int]] =
for (val i <- Iterator.range(1, n);
val j <- Iterator.range(1, i-1);
isPrime(i+j)) yield Pair(i, j)
def sum(xs: List[Double]): Double =
xs.foldLeft(0.0) { (x, y) => x + y }
def scalProd(xs: List[Double], ys: List[Double]) =
sum(for(val Pair(x, y) <- xs zip ys) yield x * y)
type Lst = List[Any]
val prefix = null
val scope = TopScope
val books = List(
Elem(prefix, "book", e, scope,
Elem(prefix, "title", e, scope,
Text("Structure and Interpretation of Computer Programs")),
Elem(prefix, "author", e, scope,
Text("Abelson, Harald")),
Elem(prefix, "author", e, scope,
Text("Sussman, Gerald J."))),
Elem(prefix, "book", e, scope,
Elem(prefix, "title", e, scope,
Text("Principles of Compiler Design")),
Elem(prefix, "author", e, scope,
Text("Aho, Alfred")),
Elem(prefix, "author", e, scope,
Text("Ullman, Jeffrey"))),
Elem(prefix, "book", e, scope,
Elem(prefix, "title", e, scope,
Text("Programming in Modula-2")),
Elem(prefix, "author", e, scope,
Text("Wirth, Niklaus")))
)
def findAuthor(books: Lst) =
for (val Elem(_, "book", _, _, book @ _*) <- books;
val Elem(_, "title", _, _, Text(title)) <- book.toList;
(title indexOf "Program") >= 0;
val Elem(_, "author", _, _, Text(author)) <- List(book)) yield author
for (val Elem(_, "book", _, _, book @ _*) <- books;
val Elem(_, "author", _, _, Text(author)) <- book.toList;
author startsWith "Ullman";
val Elem(_, "title", _, _, Text(title)) <- List(book)) yield title
removeDuplicates(
for (val Elem(_, "book", _, _, b1 @ _* ) <- books;
val Elem(_, "book", _, _, b2 @ _*) <- books;
b1 != b2;
val Elem(_, "author", _, _, Text(a1)) <- b1.toList;
val Elem(_, "author", _, _, Text(a2)) <- b2.toList;
a1 == a2) yield Pair(a1, a2))
def removeDuplicates[a](xs: List[a]): List[a] =
if (xs.isEmpty)
xs
else
xs.head :: removeDuplicates(for (val x <- xs.tail; x != xs.head) yield x)
def main(args: Array[String]) = {
Console.print("Persons over 20:")
printOlderThan20(persons) foreach { x => Console.print(" " + x) }
Console.println
Console.println("divisors(34) = " + divisors(34))
Console.print("findNums(15) =");
findNums(15) foreach { x => Console.print(" " + x); }
Console.println
val xs = List(3.5, 5.0, 4.5)
Console.println("average(" + xs + ") = " + sum(xs) / xs.length)
val ys = List(2.0, 1.0, 3.0)
Console.println("scalProd(" + xs + ", " + ys +") = " + scalProd(xs, ys))
}
}
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