Merge pull request #1761 from dotty-staging/topic/product-show

[REPL] Add show capability to common types

1 files changed, 102 insertions, 0 deletions

diff --git a/library/src/dotty/Show.scala b/library/src/dotty/Show.scala
new file mode 100644
index 000000000..2feeb29ef
--- /dev/null
+++ b/library/src/dotty/Show.scala
@@ -0,0 +1,102 @@
+package dotty
+
+import scala.annotation.implicitNotFound
+
+@implicitNotFound("No member of type class Show could be found for ${T}")
+trait Show[-T] {
+  def show(t: T): String
+}
+
+/** Ideally show would only contain `defaultShow` and the pimped generic class,
+  * but since we can't change the current stdlib, we're stuck with providing
+  * default instances in this object
+  */
+object Show {
+  private[this] val defaultShow: Show[Any] = new Show[Any] {
+    def show(x: Any) = x.toString
+  }
+
+  /** This class implements pimping of all types to provide a show method.
+    * Currently it is quite permissive, if there's no instance of `Show[T]` for
+    * any `T`, we default to `T#toString`.
+    */
+  implicit class ShowValue[V](val v: V) extends AnyVal {
+    def show(implicit ev: Show[V] = defaultShow): String =
+      ev.show(v)
+  }
+
+  implicit val stringShow: Show[String] = new Show[String] {
+    // From 2.12 spec, `charEscapeSeq`:
+    // ‘\‘ (‘b‘ | ‘t‘ | ‘n‘ | ‘f‘ | ‘r‘ | ‘"‘ | ‘'‘ | ‘\‘)
+    def show(str: String) =
+      "\"" + {
+        val sb = new StringBuilder
+        str.foreach {
+          case '\b' => sb.append("\\b")
+          case '\t' => sb.append("\\t")
+          case '\n' => sb.append("\\n")
+          case '\f' => sb.append("\\f")
+          case '\r' => sb.append("\\r")
+          case '\'' => sb.append("\\'")
+          case '\"' => sb.append("\\\"")
+          case c => sb.append(c)
+        }
+        sb.toString
+      } + "\""
+  }
+
+  implicit val intShow: Show[Int] = new Show[Int] {
+    def show(i: Int) = i.toString
+  }
+
+  implicit val floatShow: Show[Float] = new Show[Float] {
+    def show(f: Float) = f + "f"
+  }
+
+  implicit val doubleShow: Show[Double] = new Show[Double] {
+    def show(d: Double) = d.toString
+  }
+
+  implicit val charShow: Show[Char] = new Show[Char] {
+    def show(c: Char) = "'" + (c match {
+      case '\b' => "\\b"
+      case '\t' => "\\t"
+      case '\n' => "\\n"
+      case '\f' => "\\f"
+      case '\r' => "\\r"
+      case '\'' => "\\'"
+      case '\"' => "\\\""
+      case c    => c
+    }) + "'"
+  }
+
+  implicit def showList[T](implicit st: Show[T]): Show[List[T]] = new Show[List[T]] {
+    def show(xs: List[T]) =
+      if (xs.isEmpty) "Nil"
+      else "List(" + xs.map(_.show).mkString(", ") + ")"
+  }
+
+  implicit val showNil: Show[Nil.type] = new Show[Nil.type] {
+    def show(xs: Nil.type) = "Nil"
+  }
+
+  implicit def showOption[T](implicit st: Show[T]): Show[Option[T]] = new Show[Option[T]] {
+    def show(ot: Option[T]): String = ot match {
+      case Some(t) => "Some("+ st.show(t) + ")"
+      case none => "None"
+    }
+  }
+
+  implicit val showNone: Show[None.type] = new Show[None.type] {
+    def show(n: None.type) = "None"
+  }
+
+  implicit def showMap[K,V](implicit sk: Show[K], sv: Show[V]): Show[Map[K,V]] = new Show[Map[K,V]] {
+    def show(m: Map[K, V]) =
+      "Map(" + m.map { case (k, v) => sk.show(k) + " -> " + sv.show(v) } .mkString (", ") + ")"
+  }
+
+  implicit def showMapOfNothing: Show[Map[Nothing,Nothing]] = new Show[Map[Nothing,Nothing]] {
+    def show(m: Map[Nothing, Nothing]) = m.toString
+  }
+}