我正在使用Scala Combinators创建解析器。太棒了。我最终得到的是一长串陷入困境的案例类，例如：ClassDecl(Complex,List(VarDecl(Real,float), VarDecl(Imag,float)))，只需要100倍。我想知道是否有一种很好的方法以树状方式打印这样的案例类，以便更容易阅读..？ （或其他形式的漂亮印刷品）
ClassDecl
name = Complex
fields =
- VarDecl
name = Real
type = float
- VarDecl
name = Imag
type = float
我想结束这样的事情
编辑：奖金问题
是否还有一种方法来显示参数的名称..？喜欢：ClassDecl(name=Complex, fields=List( ... )？
查看名为sext的小型扩展库。它完全出于这样的目的出口these two functions。
以下是它如何用于您的示例：
object Demo extends App {
import sext._
case class ClassDecl( kind : Kind, list : List[ VarDecl ] )
sealed trait Kind
case object Complex extends Kind
case class VarDecl( a : Int, b : String )
val data = ClassDecl(Complex,List(VarDecl(1, "abcd"), VarDecl(2, "efgh")))
println("treeString output:\n")
println(data.treeString)
println()
println("valueTreeString output:\n")
println(data.valueTreeString)
}
以下是该计划的输出：
treeString output:
ClassDecl:
- Complex
- List:
| - VarDecl:
| | - 1
| | - abcd
| - VarDecl:
| | - 2
| | - efgh
valueTreeString output:
- kind:
- list:
| - - a:
| | | 1
| | - b:
| | | abcd
| - - a:
| | | 2
| | - b:
| | | efgh
使用com.lihaoyi.pprint库。
libraryDependencies += "com.lihaoyi" %% "pprint" % "0.4.1"
val data = ...
val str = pprint.tokenize(data).mkString
println(str)
您还可以配置宽度，高度，缩进和颜色：
pprint.tokenize(data, width = 80).mkString
就像解析器组合器一样，Scala已经在标准库中包含了漂亮的打印机组合器。如果您需要解决方案“反射”或者您希望明确构建打印机，那么您在问题中并没有明确说明。 （虽然你的“红利问题”暗示你可能想要“反思”解决方案）
无论如何，如果您想使用普通的Scala库开发简单漂亮的打印机，这里就是。以下代码是REPLable。
case class VarDecl(name: String, `type`: String)
case class ClassDecl(name: String, fields: List[VarDecl])
import scala.text._
import Document._
def varDoc(x: VarDecl) =
nest(4, text("- VarDecl") :/:
group("name = " :: text(x.name)) :/:
group("type = " :: text(x.`type`))
)
def classDoc(x: ClassDecl) = {
val docs = ((empty:Document) /: x.fields) { (d, f) => varDoc(f) :/: d }
nest(2, text("ClassDecl") :/:
group("name = " :: text(x.name)) :/:
group("fields =" :/: docs))
}
def prettyPrint(d: Document) = {
val writer = new java.io.StringWriter
d.format(1, writer)
writer.toString
}
prettyPrint(classDoc(
ClassDecl("Complex", VarDecl("Real","float") :: VarDecl("Imag","float") :: Nil)
))
奖金问题：将打印机包装成类型类，以实现更好的可组合性。
import java.lang.reflect.Field
...
/**
* Pretty prints case classes with field names.
* Handles sequences and arrays of such values.
* Ideally, one could take the output and paste it into source code and have it compile.
*/
def prettyPrint(a: Any): String = {
// Recursively get all the fields; this will grab vals declared in parents of case classes.
def getFields(cls: Class[_]): List[Field] =
Option(cls.getSuperclass).map(getFields).getOrElse(Nil) ++
cls.getDeclaredFields.toList.filterNot(f =>
f.isSynthetic || java.lang.reflect.Modifier.isStatic(f.getModifiers))
a match {
// Make Strings look similar to their literal form.
case s: String =>
'"' + Seq("\n" -> "\\n", "\r" -> "\\r", "\t" -> "\\t", "\"" -> "\\\"", "\\" -> "\\\\").foldLeft(s) {
case (acc, (c, r)) => acc.replace(c, r) } + '"'
case xs: Seq[_] =>
xs.map(prettyPrint).toString
case xs: Array[_] =>
s"Array(${xs.map(prettyPrint) mkString ", "})"
// This covers case classes.
case p: Product =>
s"${p.productPrefix}(${
(getFields(p.getClass) map { f =>
f setAccessible true
s"${f.getName} = ${prettyPrint(f.get(p))}"
}) mkString ", "
})"
// General objects and primitives end up here.
case q =>
Option(q).map(_.toString).getOrElse("¡null!")
}
}
我发现最好，最简洁的“开箱即用”盒子体验是与Kiama pretty printing library。它不打印成员名称而不使用额外的组合器，但只有import org.kiama.output.PrettyPrinter._; pretty(any(data))你有一个很好的开始：
case class ClassDecl( kind : Kind, list : List[ VarDecl ] )
sealed trait Kind
case object Complex extends Kind
case class VarDecl( a : Int, b : String )
val data = ClassDecl(Complex,List(VarDecl(1, "abcd"), VarDecl(2, "efgh")))
import org.kiama.output.PrettyPrinter._
// `w` is the wrapping width. `1` forces wrapping all components.
pretty(any(data), w=1)
生产：
ClassDecl (
Complex (),
List (
VarDecl (
1,
"abcd"),
VarDecl (
2,
"efgh")))
请注意，这只是最基本的例子。 Kiama PrettyPrinter是一个功能非常强大的库，具有丰富的组合器，专为智能间距，换行，嵌套和分组而设计。根据您的需求调整非常容易。截至本帖子，它在SBT中可用：
libraryDependencies += "com.googlecode.kiama" %% "kiama" % "1.8.0"
用反射
import scala.reflect.ClassTag
import scala.reflect.runtime.universe._
object CaseClassBeautifier {
def getCaseAccessors[T: TypeTag] = typeOf[T].members.collect {
case m: MethodSymbol if m.isCaseAccessor => m
}.toList
def nice[T:TypeTag](x: T)(implicit classTag: ClassTag[T]) : String = {
val instance = x.asInstanceOf[T]
val mirror = runtimeMirror(instance.getClass.getClassLoader)
val accessors = getCaseAccessors[T]
var res = List.empty[String]
accessors.foreach { z ⇒
val instanceMirror = mirror.reflect(instance)
val fieldMirror = instanceMirror.reflectField(z.asTerm)
val s = s"${z.name} = ${fieldMirror.get}"
res = s :: res
}
val beautified = x.getClass.getSimpleName + "(" + res.mkString(", ") + ")"
beautified
}
}
启动Scala 2.13，case classes（这是Product的一个实现）现在提供了一个productElementNames方法，它返回一个迭代器的字段名称。
结合提供案例类值的Product::productIterator，我们有一种简单的方法可以在不需要反射的情况下打印案例类：
def pprint(obj: Any, depth: Int = 0, paramName: Option[String] = None): Unit = {
val indent = " " * depth
val prettyName = paramName.fold("")(x => s"$x: ")
val ptype = obj match { case _: Iterable[Any] => "" case obj: Product => obj.productPrefix case _ => obj.toString }
println(s"$indent$prettyName$ptype")
obj match {
case seq: Iterable[Any] =>
seq.foreach(pprint(_, depth + 1))
case obj: Product =>
(obj.productIterator zip obj.productElementNames)
.foreach { case (subObj, paramName) => pprint(subObj, depth + 1, Some(paramName)) }
case _ =>
}
}
适合您的具体情况：
// sealed trait Kind
// case object Complex extends Kind
// case class VarDecl(a: Int, b: String)
// case class ClassDecl(kind: Kind, decls: List[VarDecl])
val data = ClassDecl(Complex, List(VarDecl(1, "abcd"), VarDecl(2, "efgh")))
pprint(data)
生产：
ClassDecl
kind: Complex
decls:
VarDecl
a: 1
b: abcd
VarDecl
a: 2
b: efgh
这是@F的无耻复制粘贴。 P自由，但是
java.sql.Timestamp的支持（因为我在Spark中使用了很多）然后！
import java.lang.reflect.Field
import java.sql.Timestamp
def prettyPrint(a: Any, indentSize: Int = 0): String = {
// Recursively get all the fields; this will grab vals declared in parents of case classes.
def getFields(cls: Class[_]): List[Field] =
Option(cls.getSuperclass).map(getFields).getOrElse(Nil) ++
cls.getDeclaredFields.toList.filterNot(f =>
f.isSynthetic || java.lang.reflect.Modifier.isStatic(f.getModifiers))
val indent = List.fill(indentSize)(" ").mkString
val newIndentSize = indentSize + 2
(a match {
// Make Strings look similar to their literal form.
case string: String =>
val conversionMap = Map('\n' -> "\\n", '\r' -> "\\r", '\t' -> "\\t", '\"' -> "\\\"", '\\' -> "\\\\")
string.map(c => conversionMap.getOrElse(c, c)).mkString("\"", "", "\"")
case xs: Seq[_] =>
xs.map(prettyPrint(_, newIndentSize)).toString
case xs: Array[_] =>
s"Array(${xs.map(prettyPrint(_, newIndentSize)).mkString(", ")})"
case map: Map[_, _] =>
s"Map(\n" + map.map {
case (key, value) => " " + prettyPrint(key, newIndentSize) + " -> " + prettyPrint(value, newIndentSize)
}.mkString(",\n") + "\n)"
case None => "None"
case Some(x) => "Some(" + prettyPrint(x, newIndentSize) + ")"
case timestamp: Timestamp => "new Timestamp(" + timestamp.getTime + "L)"
case p: Product =>
s"${p.productPrefix}(\n${
getFields(p.getClass).map { f =>
f.setAccessible(true)
s" ${f.getName} = ${prettyPrint(f.get(p), newIndentSize)}"
}
.mkString(",\n")
}\n)"
// General objects and primitives end up here.
case q =>
Option(q).map(_.toString).getOrElse("null")
})
.split("\n", -1).mkString("\n" + indent)
}
EG
case class Foo(bar: String, bob: Int)
case class Alice(foo: Foo, opt: Option[String], opt2: Option[String])
scala> prettyPrint(Alice(Foo("hello world", 10), Some("asdf"), None))
res6: String =
Alice(
foo = Foo(
bar = "hello world",
bob = 10
),
opt = Some("asdf"),
opt2 = None
)