summaryrefslogtreecommitdiff
path: root/docs/examples/monads
diff options
context:
space:
mode:
authormichelou <michelou@epfl.ch>2006-03-08 10:08:03 +0000
committermichelou <michelou@epfl.ch>2006-03-08 10:08:03 +0000
commitc44a597469fcd3549618348ad9808d923a1c9c2c (patch)
tree4f889d88e69cb0c8cd0a528d3f2f97529d60ff80 /docs/examples/monads
parent8a9572b96be66414598ca9d27b29f5f3867f2023 (diff)
downloadscala-c44a597469fcd3549618348ad9808d923a1c9c2c.tar.gz
scala-c44a597469fcd3549618348ad9808d923a1c9c2c.tar.bz2
scala-c44a597469fcd3549618348ad9808d923a1c9c2c.zip
adapted some more examples to Scala 2
Diffstat (limited to 'docs/examples/monads')
-rw-r--r--docs/examples/monads/errorInterpreter.scala70
1 files changed, 35 insertions, 35 deletions
diff --git a/docs/examples/monads/errorInterpreter.scala b/docs/examples/monads/errorInterpreter.scala
index 05dc979621..4edb5caf88 100644
--- a/docs/examples/monads/errorInterpreter.scala
+++ b/docs/examples/monads/errorInterpreter.scala
@@ -1,47 +1,47 @@
object errorInterpreter {
trait M[A] {
- def show: String;
- def bind[B](k: A => M[B]);
- def map[B](f: A => B): M[B] = bind(x => unitM(f(x)));
- def flatMap[B](f: A => M[B]): M[B] = bind(f);
+ def show: String
+ def bind[B](k: A => M[B]): M[B]
+ def map[B](f: A => B): M[B] = bind(x => unitM(f(x)))
+ def flatMap[B](f: A => M[B]): M[B] = bind(f)
}
- def unitM[A](a: A): M[A] = new Suc(a);
- def errorM[A](msg: String): M[A] = new Err(msg);
+ def unitM[A](a: A): M[A] = new Suc(a)
+ def errorM[A](msg: String): M[A] = new Err(msg)
- def showM(m: M[Value]): String = m.show;
+ def showM(m: M[Value]): String = m.show
- class Suc[A](x: T) extends M[A] {
- def bind[A](k: A => M[B]): M[B] = k(x);
- def show: String = "Success: " + x;
+ class Suc[A](x: A) extends M[A] {
+ def bind[B](k: A => M[B]): M[B] = k(x)
+ def show: String = "Success: " + x
}
- class Err[T](msg: String) extends M[T] {
- def bind[A](k: A => M[B]): M[B] = new Err(msg);
- def show: String = "Error: " + msg;
+ class Err[A](msg: String) extends M[A] {
+ def bind[B](k: A => M[B]): M[B] = new Err(msg)
+ def show: String = "Error: " + msg
}
- type Name = String;
+ type Name = String
- trait Term;
- case class Var(x: Name) extends Term;
- case class Con(n: int) extends Term;
- case class Add(l: Term, r: Term) extends Term;
- case class Lam(x: Name, body: Term) extends Term;
- case class App(fun: Term, arg: Term) extends Term;
+ trait Term
+ case class Var(x: Name) extends Term
+ case class Con(n: int) extends Term
+ case class Add(l: Term, r: Term) extends Term
+ case class Lam(x: Name, body: Term) extends Term
+ case class App(fun: Term, arg: Term) extends Term
- trait Value;
+ trait Value
case object Wrong extends Value {
- override def toString() = "wrong"
+ override def toString() = "wrong"
}
case class Num(n: int) extends Value {
- override def toString() = n.toString();
+ override def toString() = n.toString()
}
case class Fun(f: Value => M[Value]) extends Value {
override def toString() = "<function>"
}
- type Environment = List[Pair[Name, Value]];
+ type Environment = List[Pair[Name, Value]]
def lookup(x: Name, e: Environment): M[Value] = e match {
case List() => errorM("unbound variable: " + x);
@@ -55,32 +55,32 @@ object errorInterpreter {
def apply(a: Value, b: Value): M[Value] = a match {
case Fun(k) => k(b)
- case _ => errorM("should be function: " + a);
+ case _ => errorM("should be function: " + a)
}
def interp(t: Term, e: Environment): M[Value] = t match {
case Var(x) => lookup(x, e)
case Con(n) => unitM(Num(n))
case Add(l, r) => for (val a <- interp(l, e);
- val b <- interp(r, e);
- val c <- add(a, b))
+ val b <- interp(r, e);
+ val c <- add(a, b))
yield c
case Lam(x, t) => unitM(Fun(a => interp(t, Pair(x, a) :: e)))
case App(f, t) => for (val a <- interp(f, e);
- val b <- interp(t, e);
- val c <- apply(a, b))
- yield c
+ val b <- interp(t, e);
+ val c <- apply(a, b))
+ yield c
}
def test(t: Term): String =
- showM(interp(t, List()));
+ showM(interp(t, List()))
- val term0 = App(Lam("x", Add(Var("x"), Var("x"))), Add(Con(10), Con(11)));
- val term1 = App(Con(1), Con(2));
+ val term0 = App(Lam("x", Add(Var("x"), Var("x"))), Add(Con(10), Con(11)))
+ val term1 = App(Con(1), Con(2))
def main(args: Array[String]) = {
- System.out.println(test(term0));
- System.out.println(test(term1));
+ System.out.println(test(term0))
+ System.out.println(test(term1))
}
}