a pure functional implementation of finger tree based on (http:https://www.staff.city.ac.uk/~ross/papers/FingerTree.pdf) and inspired on the excellent Andrew Gibiansky's blog article (http:https://andrew.gibiansky.com/blog/haskell/finger-trees/) .

As a brief introduction, finger tree provides amortized constant time access for prepending and appending element to the tree, as well as logarithmic time concatenation and random access. Inn addition to that, combing with the Monoidal tagging on the elements, finger tree can provide a rich set of data structures built on top of it, such as priority queue, etc.

This implementation of finger tree differs from other implementations in 4 aspects:

• no third party dependencies whatsoever; that said, the cats, scalaz711 and scalaz712 compatibility are provided in separate modules.
• built with covariance in mind, which makes it interoperate with the standard Scala collection in a mich more straightforward way.
• all operations are written with absolute stack safety; no need to worry about the annoying SOE error.
• provided other data structures built on top of the Finger Tree, including a List that provides constant time append and prepend, a Vector that provides logarithmic random access to its elements, and min, max and minmax priority queues with logarithmic time pop (and constant time push).

// FingerTree
import fingers.core._
val tree = FingerTree(1,2,3,4,5)
val ptree = tree.prepend(0)
val atree = tree.append(6)
val tree2 = ptree.concat(atree)

// FList
import fingers.data.list._
val list = FList(1,2,3,4)
val plist = 0 :: list
val alist = list :+ 5
plist.headOption // --> Some(0)
alist.lastOption // --> Some(5)
// pattern match (all constant time below)
list match {
  case Nil => // ...
	case x :: xs => ...
	case xs :+ x => ...
}

// FVector
import fingers.data.vector._
val vector = FVector(1,2,3,4)
vector(0) // --> 1
vector(2) // --> 3
vector(4) // --> throw ArrayOutOfBoundException

// FMinQueue, FMaxQueue, FMinMaxQueue
val ls = List(1,4,3,2)
val fminQ = FMinQueue(ls: _*)
fminQ.toList // --> (1,2,3,4)
val fMaxQ = FMaxQueue(ls: _*)
fMaxQ.toList // --> (4,3,2,1)
val fMinMaxQ = FMinMaxQueue(ls: _*)
fMinMaxQ.toList // --> ((1,2,3,4), (4,3,2,1))

resolvers += "bintray-shengc" at "http:https://dl.bintray.com/shengc/maven"

libraryDependencies += "com.shengc" %% "fingers" % "0.0.1-77efba8" 

Due to the issue #1, build is for now only available for Scala 2.12 .