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fix calculation of number to decrement by in 'PersistentVector.delete', after additional test showed that calculation resulted in incorrect metadata. (Todo: just implement function to merge left and right subtrees.)

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This commit is contained in:
Humza Shahid
2026-01-18 00:27:03 +00:00
parent 83bb852ae2
commit 66d672505a
3 changed files with 103 additions and 59 deletions
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126
fcore/persistent-vector.sml
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@@ -548,67 +548,77 @@ struct
fun merge (left, right) = raise Fail "unimplemennted"
fun delete (start, length, tree) =
let
val finish = start + length
val matchBeforeStart = prevMatch (start, tree, 1)
val matchAfterFinish = nextMatch (finish, tree, 1)
in
if matchBeforeStart = ~1 andalso matchAfterFinish = ~1 then
empty
else if matchAfterFinish = ~1 then
(* there is no match after 'finish', so just split left.
* No need to decrement or split right,
* because the right vector would be empty. *)
splitLeft (start, tree)
else if matchBeforeStart = ~1 then
(* We don't want to use left split
* because there are no elements
* before the deletion range's 'start'.
* So we make a right split and then decrement it. *)
let
val right = splitRight (finish, tree)
in
if isEmpty right then
empty
if isEmpty tree then
empty
else
let
val finish = start + length
val matchBeforeStart = prevMatch (start, tree, 1)
val matchBeforeStart =
if matchBeforeStart >= start then
~1
else
let
val startIdx = getStartIdx right
val difference = matchAfterFinish - startIdx
in
if difference = 0 then
right
else if isEmpty right then
empty
else
decrementBy (difference, right)
end
end
else
let
val left = splitLeft (start, tree)
val right = splitRight (finish, tree)
in
if isEmpty right then
left
else
let
val leftSize = getFinishIdx left
val rightStartRelative = getStartIdx right
matchBeforeStart
val matchAfterFinish = nextMatch (finish, tree, 1)
in
if matchBeforeStart = ~1 andalso matchAfterFinish = ~1 then
empty
else if matchAfterFinish = ~1 then
(* there is no match after 'finish', so just split left.
* No need to decrement or split right,
* because the right vector would be empty. *)
splitLeft (start, tree)
else if matchBeforeStart = ~1 then
(* We don't want to use left split
* because there are no elements
* before the deletion range's 'start'.
* So we make a right split and then decrement it. *)
let
val right = splitRight (finish, tree)
in
if isEmpty right then
empty
else
let
val startIdx = getStartIdx right
val shouldBeStartIdx = matchAfterFinish - length
val difference = startIdx - shouldBeStartIdx
in
if difference = 0 then
right
else if isEmpty right then
empty
else
decrementBy (difference, right)
end
end
else
let
val left = splitLeft (start, tree)
val right = splitRight (finish, tree)
in
if isEmpty right then
left
else
let
val leftSize = getFinishIdx left
val rightStartRelative = getStartIdx right
val rightStartAbsolute = leftSize + rightStartRelative
val rightStartAbsolute = leftSize + rightStartRelative
val difference = matchAfterFinish - rightStartAbsolute
in
if difference = 0 then
merge (left, right)
else
let
val right = decrementBy (difference, right)
in
val shouldBeStartIdx = matchAfterFinish - length
val difference = rightStartAbsolute - shouldBeStartIdx
in
if difference = 0 then
merge (left, right)
end
end
end
end
else
let
val right = decrementBy (difference, right)
in
merge (left, right)
end
end
end
end
(* functions only for testing *)
fun fromListLoop (lst, acc) =