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Diffstat (limited to 'docs/examples/expressions')
-rw-r--r-- | docs/examples/expressions/expressions-current.scala | 67 |
1 files changed, 67 insertions, 0 deletions
diff --git a/docs/examples/expressions/expressions-current.scala b/docs/examples/expressions/expressions-current.scala new file mode 100644 index 0000000000..91e5df02ae --- /dev/null +++ b/docs/examples/expressions/expressions-current.scala @@ -0,0 +1,67 @@ +package examples.expressions; + +abstract class Lang { + trait Visitor { + def caseNum(n: int): unit; + } + + abstract class Exp { + def visit(v: visitor): unit; + } + + type visitor <: Visitor; + + class Num(n: int) extends Exp { + def visit(v: visitor): unit = v.caseNum(n); + } + + class Eval(result: Ref[int]): visitor extends Visitor { + def caseNum(n: int) = result.elem = n; + } +} + +abstract class Lang2 extends Lang { + abstract class Visitor2 extends Visitor { + def casePlus(left: Exp, right: Exp): unit; + } + + type visitor <: Visitor2; + + class Plus(l: Exp, r: Exp) extends Exp { + def visit(v: visitor): unit = v.casePlus(l, r); + } + + class Eval2(result: Ref[int]): visitor extends Eval(result) with Visitor2 { + def casePlus(l: Exp, r: Exp) = + result.elem = { l.visit(this); result.elem } + { r.visit(this); result.elem } + } + + class Show2(result: Ref[String]): visitor extends Visitor2 { + def caseNum(n: int) = result.elem = n.toString(); + def casePlus(l: Exp, r: Exp) = + result.elem = + "(" + { l.visit(this); result.elem } + + "+" + { r.visit(this); result.elem } + ")"; + } +} + +object Main { + + def main(args: Array[String]) = { + //val l1 = new Lang { type visitor = Visitor } // not yet implemented + object l1 extends Lang { type visitor = Visitor } // workaround + val e1: l1.Exp = new l1.Num(42); + val iref = new Ref(0); + Console.println("eval: " + { e1.visit(new l1.Eval(iref)); iref.elem }); + + //val l2 = new Lang2 { type visitor = Visitor2 } // not yet implemented + object l2 extends Lang2 { type visitor = Visitor2 } // workaround + val e2: l2.Exp = new l2.Plus(new l2.Num(5), new l2.Num(37)); + val sref = new Ref(""); + Console.println("eval: " + { e2.visit(new l2.Eval2(iref)); iref.elem }); + Console.println("show: " + { e2.visit(new l2.Show2(sref)); sref.elem }); + e1.visit(new l1.Eval(iref)); + e2.visit(new l2.Show2(sref)); + } +} + |