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begin reimplementing persistent-vector.sml's 'helpInsert' function so that it uses rope-like metadata

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This commit is contained in:
Humza Shahid
2025-12-05 10:11:06 +00:00
parent 237d9f8a38
commit 343951948c
1 changed files with 83 additions and 1 deletions
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84
fcore/persistent-vector.sml
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@@ -359,6 +359,87 @@ struct
LEAF (_, sizes) => Vector.sub (sizes, Vector.length sizes - 1)
| BRANCH (_, sizes) => Vector.sub (sizes, Vector.length sizes - 1)
fun helpInsert (start, finish, tree) =
case tree of
BRANCH (nodes, sizes) =>
if finish >= Vector.sub (sizes, Vector.length sizes - 1) then
(* we want to append *)
let
val prevSize =
if Vector.length sizes > 1 then
Vector.sub (sizes, Vector.length sizes - 1)
else
0
val descendStart = start - prevSize
val descendFinish = finish - prevSize
val descendNode = Vector.sub (nodes, Vector.length nodes - 1)
in
case helpAppend (descendStart, descendFinish, descendNode) of
UPDATE newLast =>
let
val sizes = Vector.update (sizes, Vector.length sizes - 1, finish)
val nodes = Vector.update (nodes, Vector.length nodes - 1, newLast)
in
INSERT_UPDATE (BRANCH (nodes, sizes))
end
| APPEND newLast =>
if Vector.length nodes > maxSize then
(* we have to split *)
let
val leftLen = SOME halfSize
val rightLen = SOME (Vector.length nodes - halfSize)
val leftNodeSlice = VectorSlice.slice (nodes, 0, leftLen)
val leftSizeSlice = VectorSlice.slice (sizes, 0, leftLen)
val leftNodes = VectorSlice.vector leftNodeSlice
val leftSizes = VectorSlice.vector leftSizeSlice
val rightNodeSlice =
VectorSlice.slice (nodes, halfSize, rightLen)
val rightSizeSlice =
VectorSlice.slice (sizes, halfSize, rightLen)
val rightNodes =
VectorSlice.concat [rightNodeSlice, VectorSlice.full #[newLast]]
val rightSizes =
let
(* we want to maintain relative indexing metadata
* so that each vector only considers the metadata of its
* own nodes.
* So, we need to subtract the maximum sizes of the leftSizes
* from every size on the right node, to maintain relative
* indexing metadata *)
val maxLeftSize = Vector.sub (leftSizes, Vector.length leftSizes - 1)
val maxRightSize = Vector.sub (sizes, Vector.length sizes - 1)
val finish = finish + maxRightSize
in
Vector.tabulate (VectorSlice.length rightSizeSlice + 1,
fn i =>
if i < VectorSlice.length rightSizeSlice then
Vector.sub (rightSizeSlice, i) - maxLeftSize
else
finish)
end
val left = BRANCH (leftNodes, leftSizes)
val right = BRANCH (rightNodes, rightSizes)
in
INSERT_SPLIT (left, right)
end
else
(* append newLast to current node *)
let
val newLast = #[newLast]
val finish =
#[Vector.sub (sizes, Vector.length sizes - 1) + finish]
val nodes = Vector.concat [nodes, newLast]
val sizes = Vector.concat [sizes, finish]
in
INSERT_UPDATE (BRANCH (nodes, sizes))
end
end
fun helpInsert (start, finish, tree) =
case tree of
BRANCH (nodes, sizes) =>
@@ -626,7 +707,8 @@ struct
INSERT_UPDATE tree => tree
| INSERT_SPLIT (left, right) =>
let
val sizes = #[getMaxSize left, getMaxSize right]
val leftSize = getMaxSize left
val sizes = #[leftSize, leftSize + getMaxSize right]
val nodes = #[left, right]
in
BRANCH (nodes, sizes)