Drilling through the expendables.

This is pretty handy:

scala> Array(1, 2, 3) transitiveClosure (x => Direct(x.m.init, x.m.tail)) mk_s ", "
res0: psp.std.String = [ 1, 2, 3 ], [ 1, 2 ], [ 1 ], [  ], [ 2 ], [ 2, 3 ], [ 3 ]

scala> path("/l/src") transitiveClosure (_.subdirectories) take 5 >
/l/src
/l/src/coq
/l/src/coq/Kopitiam
/l/src/coq/Kopitiam/.git
/l/src/coq/Kopitiam/.git/hooks

// Sigh, https://issues.scala-lang.org/browse/SI-8936
scala> classOf[List[_]] transitiveClosure (_.getInterfaces)
<console>:31: error: type mismatch;
 found   : Array[Class[_]]
 required: psp.std.pSeq[psp.std.Class[_$1]] where type _$1 <: psp.std.List[_]
    (which expands to)  psp.std.api.Foreach[Class[_$1]]
              classOf[List[_]] transitiveClosure (_.getInterfaces)
                                                    ^

// I made a wrapper class to avoid the useless existential.
scala> pClassOf[List[_]] transitiveClosure (_.getInterfaces) >
class scala.collection.immutable.List
interface scala.collection.immutable.LinearSeq
interface scala.collection.immutable.Seq
interface scala.collection.immutable.Iterable
interface scala.collection.immutable.Traversable
interface scala.collection.Traversable
interface scala.collection.TraversableLike
interface scala.collection.generic.HasNewBuilder
interface scala.collection.generic.FilterMonadic
interface scala.collection.TraversableOnce
interface scala.collection.GenTraversableOnce
interface scala.collection.GenTraversableLike
interface scala.collection.Parallelizable
interface scala.collection.GenTraversable
interface scala.collection.generic.GenericTraversableTemplate
interface scala.Immutable
interface scala.collection.Iterable
interface scala.collection.GenIterable
interface scala.collection.GenIterableLike
interface scala.collection.IterableLike
interface scala.Equals
interface scala.collection.Seq
interface scala.PartialFunction
interface scala.Function1
interface scala.collection.GenSeq
interface scala.collection.GenSeqLike
interface scala.collection.SeqLike
interface scala.collection.LinearSeq
interface scala.collection.LinearSeqLike
interface scala.Product
interface scala.collection.LinearSeqOptimized
interface java.io.Serializable