Scala Pattern Matching pretty printed

Question

Is that possible to somehow marshall PartialFunction (let's assume it will always contains only one case) into something human-readable?

Let's say we have collection of type Any (messages: List[Any]) and number of PartialFuntion[Any, T] defined using pattern matching block.

case object R1
case object R2
case object R3

val pm1: PartialFunction[Any, Any] = {
  case "foo" => R1
}

val pm2: PartialFunction[Any, Any] = {
  case x: Int if x > 10 => R2
}

val pm3: PartialFunction[Any, Any] = {
  case x: Boolean => R3
}

val messages: List[Any] = List("foo", 20)
val functions = List(pm1, pm2)

then we can find all the messages matched by provided PFs and related applications

val found: List[Option[Any]] = functions map { f =>
  messages.find(f.isDefined).map(f)
}

but what if I need resulting map of 'what I expect' to 'what I've got' in the human-readable form (for logging). Say,

(case "foo")         -> Some(R1)
(case Int if _ > 10) -> Some(R2)
(case Boolean)       -> None

Is that possible? Some macro/meta works?

Answer 1

There's nothing at runtime which will print compiled code nicely.

You could write a macro which will print the source code of the tree and use that? Most macro tutorials start with a macro for printing source code -- see e.g. http://www.warski.org/blog/2012/12/starting-with-scala-macros-a-short-tutorial/

Perhaps:

// Given a partial function "pf", return the source code for pf
// as a string as well as the compiled, runnable function itself
def functionAndSource(pf: PartialFunction[Any, Any]): (String, PartialFunction[Any, Any]) = macro functionAndSourceImpl

def functionAndSourceImpl ...

val pm1: (String, PartialFunction[Any, Any]) = functionAndSource {
  case "foo" => R1
}

This isn't ever going to be that easy or nice in Scala. Scala isn't Lisp or Ruby: it's a compiled language and it is not optimised for reflection on the code itself.