collections addPrototype: #Cord derivedFrom: {Sequence}.
Cord addSlot: #split. "The index where the second half begins."
Cord addSlot: #firstBranch. "The first half of the cord."
Cord addSlot: #secondBranch. "The latter half of the cord."
Cord addSlot: #depth valued: 1. "The default for a couple of strings ;;'d."
Cord addSlot: #size. "The incrementally-calculated Cord size."

c1@(Sequence traits) ;; c2@(Sequence traits)
"Build a cord out of any 2 sequences."
[| newC |
  c1 isEmpty
    ifTrue: [^ c2].
  c2 isEmpty
    ifTrue: [^ c1].
  newC: Cord clone.
  newC split: c1 size.
  newC firstBranch: c1.
  newC secondBranch: c2.
  newC size: c1 size + c2 size.
  newC
].

c1@(Sequence traits) ;; c2@(Cord traits)
"Set up the depth if the second element is a cord."
[| newC |
  newC: resend.
  newC depth: c2 depth + 1.
  newC
].

c1@(Cord traits) ;; c2@(Sequence traits)
"Set up the depth if the first element is a cord."
[| newC |
  newC: resend.
  newC depth: c1 depth + 1.
  newC
].

c1@(Cord traits) ;; c2@(Cord traits)
"If both are cords, the deepest counts for the depth."
[| newC |
  newC: resend.
  newC depth: (c1 depth max: c2 depth) + 1.
  newC
].

c@(Cord traits) at: n
"Recursively descend the tree to find the element in the base sequences.
Since this is ~O(log n) vs O(0), iterators need to avoid this and use do:
or doWithIndex:."
[
  n < c split
    ifTrue: [c firstBranch at: n]
    ifFalse: [c secondBranch at: n - split]
].

c@(Cord traits) do: block
"The major premise of this override is to avoid calling at: for each index,
since it is more expensive for Cords to perform."
[
  c firstBranch do: block.
  c secondBranch do: block.
  c
].

c@(Cord traits) doWithIndex: block
"Simulate an index during the traversal."
[| idx |
  idx: 0.
  c do: [| :each | block applyWith: each with: idx.
	 idx: idx + 1].
  c
].

c@(Cord traits) as: sc@(Sequence traits)
[| newSC |
  newSC: (sc newSizeOf: c).
  c doWithIndex: [| :each :index | newSC at: index put: each].
  newSC
].

c@(Cord traits) as: sc@(ExtensibleArray traits)
[| newOC |
  newOC: (oc newSizeOf: c).
  newOC addAllLast: c.
  newOC
].

c@(Cord traits) shouldBeFlattened
"Pick a pretty small number that statistically is easier to just make a new
sequence for, and make sure that it's not just a base Cord."
[
  c size < 20 and: [c depth >= 2]
].

c@(Cord traits) flatten
[
  c as: Array
].

c@(Cord traits) shouldBeBalanced
[
  c depth
].

c@(Cord traits) balance
[
  c notYetImplemented
].