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<h2>Comments</h2>
<pre><code>// Single line comment
/* Mutli-line
comment */</code></pre>
<h2>Strings and characters</h2>
<pre><code>'a'
"foo bar baz"
"""Multi-line
string"""</code></pre>
<h2>Numbers</h2>
<pre><code>0
21
0xFFFFFFFF
-42L
0.0
1e30f
3.14159f
1.0e-100
.1
</code></pre>
<h2>Symbols</h2>
<pre><code>'x
'identifier</code></pre>
<h2>Full example</h2>
<pre><code>// Contributed by John Williams
package examples
object lazyLib {
/** Delay the evaluation of an expression until it is needed. */
def delay[A](value: => A): Susp[A] = new SuspImpl[A](value)
/** Get the value of a delayed expression. */
implicit def force[A](s: Susp[A]): A = s()
/**
* Data type of suspended computations. (The name froms from ML.)
*/
abstract class Susp[+A] extends Function0[A]
/**
* Implementation of suspended computations, separated from the
* abstract class so that the type parameter can be invariant.
*/
class SuspImpl[A](lazyValue: => A) extends Susp[A] {
private var maybeValue: Option[A] = None
override def apply() = maybeValue match {
case None =>
val value = lazyValue
maybeValue = Some(value)
value
case Some(value) =>
value
}
override def toString() = maybeValue match {
case None => "Susp(?)"
case Some(value) => "Susp(" + value + ")"
}
}
}
object lazyEvaluation {
import lazyLib._
def main(args: Array[String]) = {
val s: Susp[Int] = delay { println("evaluating..."); 3 }
println("s = " + s) // show that s is unevaluated
println("s() = " + s()) // evaluate s
println("s = " + s) // show that the value is saved
println("2 + s = " + (2 + s)) // implicit call to force()
val sl = delay { Some(3) }
val sl1: Susp[Some[Int]] = sl
val sl2: Susp[Option[Int]] = sl1 // the type is covariant
println("sl2 = " + sl2)
println("sl2() = " + sl2())
println("sl2 = " + sl2)
}
}</code></pre>
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