Scala example source code file (bug0031.scala)

This example Scala source code file (bug0031.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Scala tags/keywords

array, assertion, assertion, boolean, boolean, ensure, ensure, list, list, main

The Scala bug0031.scala source code

object Main {

    trait Ensure[a] {
        def ensure(postcondition: a => Boolean): a
    }

    def require[a](precondition: => Boolean)(command: => a): Ensure[a] = 
        if (precondition)
            new Ensure[a] {
	        def ensure(postcondition: a => Boolean): a = {
	            val result = command;
	            if (postcondition(result)) result
	            else error("Assertion error")
                }
	    }
        else
            error("Assertion error");

    def arb[a](s: List[a]) =
        require (! s.isEmpty) {
           s.head
        } ensure (result => s contains result);

    def main(args: Array[String]) = {
    	val s = List(1, 2);
        Console.println(arb(s))
    }

}