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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
View File

@@ -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) =

33
test/persistent-vector-tests.sml
View File

@@ -342,6 +342,39 @@ struct
in
Expect.isTrue (outputList = expectedOutput)
end)
, test
"decrements subsequent elements correctly \
\when deletion range is before first element to middle element"
(fn _ =>
let
(* arrange *)
val inputList =
[ {start = 1, finish = 1}
, {start = 2, finish = 2}
, {start = 3, finish = 3}
, {start = 4, finish = 4}
, {start = 50, finish = 50}
, {start = 60, finish = 60}
, {start = 70, finish = 70}
, {start = 80, finish = 80}
]
val pv = PersistentVector.fromList inputList
(* act *)
val pv = PersistentVector.delete (0, 3, pv)
(* assert *)
val outputList = PersistentVector.toList pv
val expectedOutput =
[ {start = 1, finish = 1}
, {start = 47, finish = 47}
, {start = 57, finish = 57}
, {start = 67, finish = 67}
, {start = 77, finish = 77}
]
in
Expect.isTrue (outputList = expectedOutput)
end)
]
val tests = [appendTests, toListTests, splitLeftTests, deleteTests]

3
todo.md
View File

@@ -1,3 +1,4 @@
# To-do list
- Implement `PersistentVector.delete` and test it
- Implement function to merge left and right subtrees for `PersistentVector.delete` function
- Test `PersistentVector.delete` function
- Implement 'yj' motion and add tests for it