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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.iterator)
def printOlderThan20(xs: Iterator[Person]): Iterator[String] =
for (p <- xs if p.age > 20) yield p.name
val persons = List(
new Person("John", 40),
new Person("Richard", 68)
)
def divisors(n: Int): List[Int] =
for (i <- List.range(1, n+1) if n % i == 0) yield i
def isPrime(n: Int) = divisors(n).length == 2
def findNums(n: Int): Iterable[(Int, Int)] =
for (i <- 1 until n;
j <- 1 until (i-1);
if isPrime(i+j)) yield (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((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 (Elem(_, "book", _, _, book @ _*) <- books;
Elem(_, "title", _, _, Text(title)) <- book.toList;
if (title indexOf "Program") >= 0;
Elem(_, "author", _, _, Text(author)) <- List(book)) yield author
for (Elem(_, "book", _, _, book @ _*) <- books;
Elem(_, "author", _, _, Text(author)) <- book.toList;
if author startsWith "Ullman";
Elem(_, "title", _, _, Text(title)) <- List(book)) yield title
removeDuplicates(
for (Elem(_, "book", _, _, b1 @ _* ) <- books;
Elem(_, "book", _, _, b2 @ _*) <- books;
if b1 != b2;
Elem(_, "author", _, _, Text(a1)) <- b1.toList;
Elem(_, "author", _, _, Text(a2)) <- b2.toList;
if a1 == a2) yield Pair(a1, a2))
def removeDuplicates[a](xs: List[a]): List[a] =
if (xs.isEmpty)
xs
else
xs.head :: removeDuplicates(for (x <- xs.tail if x != xs.head) yield x)
def main(args: Array[String]) {
print("Persons over 20:")
printOlderThan20(persons) foreach { x => print(" " + x) }
println
println("divisors(34) = " + divisors(34))
print("findNums(15) =");
findNums(15) foreach { x => print(" " + x); }
println
val xs = List(3.5, 5.0, 4.5)
println("average(" + xs + ") = " + sum(xs) / xs.length)
val ys = List(2.0, 1.0, 3.0)
println("scalProd(" + xs + ", " + ys +") = " + scalProd(xs, ys))
}
}
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