小编Rou*_*ari的帖子

我正在研究DSL,我遇到了使用方法作为链中的中缀运算符的问题.我将尝试用一些代码来解释它.我有一个特质Term和案例类Literal并Variable扩展它.我想使用一些运算符构造一个术语实例列表.

case class Expr(val terms: List[Term]) {
 def +(v: String) = Expr(Literal(v) :: terms)
 def -->(func: List[String] => List[String]) = terms match {
  case Literal(v) :: ts => Expr(Variable(v, func) :: ts)
  case _ => throw new Exception("Can only apply function on literal")
 }
}

object foo {
 def bar(name: String) = Expr(Literal(name) :: Nil)
}

// some functions
val one = ... 
val all = ...

// works
foo bar "x"        
// res1: …

我正在尝试使用简单的对象数组中的jade渲染表.但是,我不想简单地为每个对象渲染一行,而是想在每一行上渲染三个对象.

<table>
  <thead>...</thead>
  <tbody>
    <tr>
      <td>obj0</td>
      <td>obj1</td>
      <td>obj2</td>
    </tr>
    <tr>
      <td>obj3</td>
      <td>obj4</td>
      <td>obj5</td>
    </tr>
    ...
  </tbody>
</table

我有一个函数,我知道是尾递归.但是由于我定义它的方式,编译器抱怨函数在非尾部位置具有递归调用.这是功能.

@tailrec
def travel: (Int, List[Char]) => Int = {
    case (n,        Nil) => n
    case (n, '~' :: sls) => travel(0, sls)
    case (n, '^' :: sls) => travel(max(n-1,0), sls)
    case (n, '>' :: sls) => travel(n+1, sls)
    case (_,  s  :: sls) => throw new IllegalArgumentException("Illegal selector '" + s + "'")
}

我明白了

error: could not optimize @tailrec annotated method travel: it contains a recursive call not in tail position
def travel: (Int, List[Char]) => Int = …