?? expressions-current.scala
字號:
package examples.expressionsclass Ref[a](var elem:a) {}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]) requires visitor extends Visitor { def caseNum(n: int) = result.elem = n }}abstract class Lang2 extends Lang { trait 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 { class Eval2(result: Ref[int]) requires 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]) requires 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]): unit = { //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)) }}?? 快捷鍵說明
復制代碼
Ctrl + C
搜索代碼
Ctrl + F
全屏模式
F11
切換主題
Ctrl + Shift + D
顯示快捷鍵
?
增大字號
Ctrl + =
減小字號
Ctrl + -