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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 books = List(
Elem("", "book", e,
Elem("", "title", e,
Text("Structure and Interpretation of Computer Programs")),
Elem("", "author", e,
Text("Abelson, Harald")),
Elem("", "author", e,
Text("Sussman, Gerald J."))),
Elem("", "book", e,
Elem("", "title", e,
Text("Principles of Compiler Design")),
Elem("", "author", e,
Text("Aho, Alfred")),
Elem("", "author", e,
Text("Ullman, Jeffrey"))),
Elem("", "book", e,
Elem("", "title", e,
Text("Programming in Modula-2")),
Elem("", "author", e,
Text("Wirth, Niklaus")))
);
def findAuthor(books: Lst) =
for (val Elem(_, "book",_,book @ _*) <- books;
val Elem(_, "title",_,Text( title )) <- book;
(title indexOf "Program") >= 0;
val Elem(_, "author",_,Text( author )) <- book) yield author;
for (val Elem(_, "book", _, b @ _*) <- books;
val Elem(_, "author", _, Text( author )) <- b;
author startsWith "Ullman";
val Elem(_, "title", _,Text( title )) <- b) yield title;
removeDuplicates(
for (val Elem(_, "book", _, b1 @ _* ) <- books;
val Elem(_, "book", _, b2 @ _*) <- books;
b1 != b2;
val Elem(_, "author",_, Text( a1 )) <- b1;
val Elem(_, "author",_, Text( a2 )) <- b2;
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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