From 0ad682f2c139a76692abab7f0b9bf1dcd6433008 Mon Sep 17 00:00:00 2001
From: Mark Harrah <dmharrah@gmail.com>
Date: Sat, 7 May 2011 22:02:06 -0400
Subject: [PATCH] basic optional input support

---
 main/Structure.scala           | 6 +++++-
 util/collection/Settings.scala | 9 +++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/main/Structure.scala b/main/Structure.scala
index 9ba0a1ef3..10e5e419f 100644
--- a/main/Structure.scala
+++ b/main/Structure.scala
@@ -145,7 +145,9 @@ object Scoped
 		final def <<= (app: Initialize[S]): Setting[S]  =  setting(scoped, app)
 
 		final def apply[T](f: S => T): Initialize[T] = Apply.single(scoped)(f)
-		def identity: Initialize[S] = apply(idFun)
+		final def identity: Initialize[S] = apply(idFun)
+		final def ? : Initialize[Option[S]] = Project.optional(scoped)(idFun)
+		final def ??[T >: S](or: => T): Initialize[T] = Project.optional(scoped)(_ getOrElse or )
 
 		final def get(settings: Settings[Scope]): Option[S] = settings.get(scope, key)
 	}
@@ -182,6 +184,8 @@ object Scoped
 		def andFinally(fin: => Unit): App[S] = mk(_ andFinally fin)
 		def doFinally(t: Task[Unit]): App[S] = mk(_ doFinally t)
 		def identity: App[S] = mk(idFun)
+		def ? : Initialize[Task[Option[S]]] = Project.optional(scoped) { case None => mktask { None }; case Some(t) => t map some.fn }
+		def ??[T >: S](or: => T): Initialize[Task[T]] = Project.optional(scoped)( _ getOrElse mktask(or) )
 
 		def || [T >: S](alt: Task[T]): App[T]  =  mk(_ || alt)
 		def && [T](alt: Task[T]): App[T]  =  mk(_ && alt)
diff --git a/util/collection/Settings.scala b/util/collection/Settings.scala
index 40d54de0d..60694120b 100644
--- a/util/collection/Settings.scala
+++ b/util/collection/Settings.scala
@@ -53,6 +53,7 @@ trait Init[Scope]
 
 	def setting[T](key: ScopedKey[T], init: Initialize[T]): Setting[T] = new Setting[T](key, init)
 	def value[T](value: => T): Initialize[T] = new Value(value _)
+	def optional[T,U](key: ScopedKey[T])(f: Option[T] => U): Initialize[U] = new Optional(Some(key), f)
 	def update[T](key: ScopedKey[T])(f: T => T): Setting[T] = new Setting[T](key, app(key :^: KNil)(hl => f(hl.head)))
 	def app[HL <: HList, T](inputs: KList[ScopedKey, HL])(f: HL => T): Initialize[T] = new Apply(f, inputs)
 	def uniform[S,T](inputs: Seq[ScopedKey[S]])(f: Seq[S] => T): Initialize[T] = new Uniform(f, inputs)
@@ -192,6 +193,14 @@ trait Init[Scope]
 		override def toString = "setting(" + key + ")"
 	}
 
+	private[this] final class Optional[S,T](a: Option[ScopedKey[S]], f: Option[S] => T) extends Initialize[T]
+	{
+		def dependsOn = a.toList
+		def map[Z](g: T => Z): Initialize[Z] = new Optional[S,Z](a, g compose f)
+		def get(map: Settings[Scope]): T = f(a map asFunction(map))
+		def mapReferenced(g: MapScoped) = new Optional(mapKey(g), f)
+		private[this] def mapKey(g: MapScoped) = try { a map g.fn } catch { case _: Uninitialized => None }
+	}
 	private[this] final class Joined[S,T,U](a: Initialize[S], b: Initialize[T], f: (S,T) => U) extends Initialize[U]
 	{
 		def dependsOn = a.dependsOn ++ b.dependsOn