from-github.txt

commit 056fe782e507fd32ae51e9ecefd0e4fca0831fe9
Author: Robin Munn <rmunn@pobox.com>
Date:   Mon Jul 29 01:53:41 2019 +0700

    WIP on making RRBVector functions transient-aware
    
    Tests are still passing so far, but we're not finished yet.
    
    The idea is that when a transient is passed to RRBVector.split (or
    whatever function), the transient is reused as much as possible, or if a
    new transient is created, its owner token is the same.

diff --git a/src/Ficus/RRBBetterVector.fs b/src/Ficus/RRBBetterVector.fs
index bc48c15..9b377ba 100644
--- a/src/Ficus/RRBBetterVector.fs
+++ b/src/Ficus/RRBBetterVector.fs
@@ -972,6 +972,8 @@ and RRBTransientVector<'T> internal (count, shift : int, root : RRBNode<'T>, tai
         elif idx > this.Count then failwith "Index must not be more than one past the end of the vector"
         else ()
 
+let internal isTransient (vec : RRBVector<'T>) = vec :? RRBTransientVector<'T>
+
 // TODO: This module is currently fully-named as Ficus.RRBVector.RRBVectorModule; is that actually what I want? Or should I
 // change the name of the second part of that name so it's something like Ficus.Vectors.RRBVectorModule?
 [<CompilationRepresentation(CompilationRepresentationFlags.ModuleSuffix)>]
@@ -1003,31 +1005,63 @@ module RRBVector =
         for item in s do
             transient <- transient.Push item :?> RRBTransientVector<'T>
         transient.Persistent() :> RRBVector<'T>
-    let inline ofArray (a : 'T[]) = a |> ofSeq // TODO: Could add a bit of efficiency by special-casing tail-only vectors here
-    let inline ofList (l : 'T list) = l |> ofSeq
+    let ofArray (a : 'T[]) =
+        if a.Length <= Literals.blockSize then
+            let tail = Array.copy a
+            RRBPersistentVector<'T>(a.Length, Literals.blockSizeShift, emptyNode, tail, 0) :> RRBVector<'T>
+        elif a.Length <= Literals.blockSize * 2 then
+            let leaf, tail = a |> Array.splitAt Literals.blockSize
+            RRBPersistentVector<'T>(a.Length, Literals.blockSizeShift, [|RRBNode<'T>.MkLeaf nullOwner leaf|] |> RRBNode<'T>.MkFullNode nullOwner, tail, Literals.blockSize) :> RRBVector<'T>
+            // TODO: Perhaps this should be a static member of RRBVector, called FromArray? Might be nice to have this in the C# API
+        else
+            a |> ofSeq
+    let inline ofList (l : 'T list) =
+        let mutable transient = RRBTransientVector<'T>.MkEmpty()
+        for item in l do
+            transient <- transient.Push item :?> RRBTransientVector<'T>
+        transient.Persistent() :> RRBVector<'T>
 
     // TODO: Try improving average and averageBy by using iterLeafArrays(), summing up each array, and then dividing by count at the end. MIGHT be faster than Seq.average.
     let inline average (vec : RRBVector<'T>) = vec |> Seq.average
     let inline averageBy f (vec : RRBVector<'T>) = vec |> Seq.averageBy f
     let choose (chooser : 'T -> 'U option) (vec : RRBVector<'T>) : RRBVector<'U> =
-        // TODO FIXME: Find everywhere where we make new transient vectors, and whenever possible make them take the owner token from the original vector
-        let mutable transient = RRBTransientVector<'U>.MkEmpty()
-        for item in vec do
-            match chooser item with
-            | None -> ()
-            | Some value -> transient <- transient.Push value :?> RRBTransientVector<_>
-        transient.Persistent() :> RRBVector<_>
-    // Alternate version. TODO: Benchmark
+        // TODO: Might be able to consolidate most of this (as we did in RRBVector.except), as only the first and last lines really differ. Ditto for rest of "if vec |> isTransient" cases
+        if vec |> isTransient then
+            let mutable result = RRBTransientVector<'U>.MkEmptyWithToken((vec :?> RRBTransientVector<'T>).Owner)
+            for item in vec do
+                match chooser item with
+                | None -> ()
+                | Some value -> result <- result.Push value :?> RRBTransientVector<_>
+            result :> RRBVector<_>
+        else
+            let mutable transient = RRBTransientVector<'U>.MkEmpty()
+            for item in vec do
+                match chooser item with
+                | None -> ()
+                | Some value -> transient <- transient.Push value :?> RRBTransientVector<_>
+            transient.Persistent() :> RRBVector<_>
+    // Alternate version (for persistent vectors only). TODO: Benchmark
     let chooseAlt (chooser : 'T -> 'U option) (vec : RRBVector<'T>) : RRBVector<'U> =
+        if vec |> isTransient then failwith "DEBUG: chooseAlt only implemented for persistent vectors"
         vec |> Seq.choose chooser |> ofSeq
 
     let chunkBySize chunkSize (vec : RRBVector<'T>) =
-        let mutable transient = RRBTransientVector<_>.MkEmpty()
-        let mutable remaining = vec
-        while remaining.Length > 0 do
-            transient <- transient.Push (remaining.Take chunkSize) :?> RRBTransientVector<_>
-            remaining <- remaining.Skip chunkSize
-        transient.Persistent() :> RRBVector<_>
+        if vec |> isTransient then
+            let mutable result = RRBTransientVector<_>.MkEmptyWithToken((vec :?> RRBTransientVector<'T>).Owner)
+            let mutable remaining = vec
+            while remaining.Length > 0 do
+                let chunk, rest = remaining.Split chunkSize
+                result <- result.Push chunk :?> RRBTransientVector<_>
+                remaining <- rest
+            result :> RRBVector<_>
+        else
+            let mutable transient = RRBTransientVector<_>.MkEmpty()
+            let mutable remaining = vec
+            while remaining.Length > 0 do
+                let chunk, rest = remaining.Split chunkSize
+                transient <- transient.Push chunk :?> RRBTransientVector<_>
+                remaining <- rest
+            transient.Persistent() :> RRBVector<_>
 
     let concat (vecs : seq<RRBVector<'T>>) =
         // TODO: Implement concatenation transient RRBVectors so this will be faster (no need to build and throw away so many intermediate result vectors)
@@ -1039,6 +1073,8 @@ module RRBVector =
             result <- result.Append vec
         result
 
+    // TODO FIXME: Find everywhere where we make new transient vectors, and whenever possible make them take the owner token from the original vector
+
     let inline collect (f : 'T -> RRBVector<'T>) (vec : RRBVector<'T>) =
         // TODO: Benchmark the following two options, because I have no idea which is slower.
         // Option 1, the merging version
@@ -1052,46 +1088,96 @@ module RRBVector =
         // transient.Persistent() :> RRBVector<'T>
 
     let inline compareWith f (vec1 : RRBVector<'T>) (vec2 : RRBVector<'T>) = (vec1, vec2) ||> Seq.compareWith f
-    let inline countBy f (vec : RRBVector<'T>) = vec |> Seq.countBy f |> ofSeq
+
+    let countBy f (vec : RRBVector<'T>) =
+        if vec |> isTransient then
+            let result = RRBTransientVector<_>.MkEmptyWithToken((vec :?> RRBTransientVector<'T>).Owner)
+            for resultItem in vec |> Seq.countBy f do
+                result.Push resultItem |> ignore
+            result :> RRBVector<_>
+        else
+            vec |> Seq.countBy f |> ofSeq
+
     let inline contains item (vec : RRBVector<'T>) = vec |> Seq.contains item
-    let inline distinct (vec : RRBVector<'T>) = vec |> Seq.distinct |> ofSeq
-    let inline distinctBy f (vec : RRBVector<'T>) = vec |> Seq.distinctBy f |> ofSeq
+
+    let distinct (vec : RRBVector<'T>) =
+        if vec |> isTransient then
+            let result = RRBTransientVector<_>.MkEmptyWithToken((vec :?> RRBTransientVector<'T>).Owner)
+            for resultItem in vec |> Seq.distinct do
+                result.Push resultItem |> ignore
+            result :> RRBVector<_>
+        else
+            vec |> Seq.distinct |> ofSeq
+
+    let distinctBy f (vec : RRBVector<'T>) =
+        if vec |> isTransient then
+            let result = RRBTransientVector<_>.MkEmptyWithToken((vec :?> RRBTransientVector<'T>).Owner)
+            for resultItem in vec |> Seq.distinctBy f do
+                result.Push resultItem |> ignore
+            result :> RRBVector<_>
+        else
+            vec |> Seq.distinctBy f |> ofSeq
+
     let inline empty<'T> = RRBPersistentVector<'T>.MkEmpty() :> RRBVector<'T>
     let exactlyOne (vec : RRBVector<'T>) =
         if vec.Length <> 1 then invalidArg "vec" <| sprintf "exactlyOne called on a vector of %d items (requires a vector of exactly 1 item)" vec.Length
         vec.Peek()
+
     let except (vec : RRBVector<'T>) (excludedVec : RRBVector<'T>) =
         let excludedSet = System.Collections.Generic.HashSet<'T>(excludedVec)
-        let mutable transient = RRBTransientVector<'T>.MkEmpty()
+        let mutable transient =
+            if vec |> isTransient
+            then RRBTransientVector<'T>.MkEmptyWithToken((vec :?> RRBTransientVector<'T>).Owner)
+            else RRBTransientVector<'T>.MkEmpty()
         for item in vec do
             if not (excludedSet.Contains item) then transient <- transient.Push item :?> RRBTransientVector<'T>
-        transient.Persistent() :> RRBVector<'T>
+        if vec |> isTransient then transient :> RRBVector<'T> else transient.Persistent() :> RRBVector<'T>
+
     let inline exists f (vec : RRBVector<'T>) = vec |> Seq.exists f
     let inline exists2 f (vec1 : RRBVector<'T>) (vec2 : RRBVector<'U>) = (vec1, vec2) ||> Seq.exists2 f
+
     let filter pred (vec : RRBVector<'T>) =
-        let mutable transient = RRBTransientVector<'T>.MkEmpty()
+        let mutable transient =
+            if vec |> isTransient
+            then RRBTransientVector<'T>.MkEmptyWithToken((vec :?> RRBTransientVector<'T>).Owner)
+            else RRBTransientVector<'T>.MkEmpty()
         for item in vec do
             if pred item then transient <- transient.Push item :?> RRBTransientVector<'T>
-        transient.Persistent() :> RRBVector<'T>
+        if vec |> isTransient then transient :> RRBVector<'T> else transient.Persistent() :> RRBVector<'T>
+
     let filteri pred (vec : RRBVector<'T>) =
-        let mutable transient = RRBTransientVector<'T>.MkEmpty()
+        let mutable transient =
+            if vec |> isTransient
+            then RRBTransientVector<'T>.MkEmptyWithToken((vec :?> RRBTransientVector<'T>).Owner)
+            else RRBTransientVector<'T>.MkEmpty()
         let mutable i = 0
         for item in vec do
             if pred i item then transient <- transient.Push item :?> RRBTransientVector<'T>
             i <- i + 1
-        transient.Persistent() :> RRBVector<'T>
+        if vec |> isTransient then transient :> RRBVector<'T> else transient.Persistent() :> RRBVector<'T>
+
     let filter2 pred (vec1 : RRBVector<'T>) (vec2 : RRBVector<'T>) =
-        let mutable transient = RRBTransientVector<'T * 'T>.MkEmpty()
+        let resultShouldBeTransient = vec1 |> isTransient && vec2 |> isTransient && isSameObj (vec1 :?> RRBTransientVector<'T>).Owner (vec2 :?> RRBTransientVector<'T>).Owner
+        let mutable transient =
+            if resultShouldBeTransient
+            then RRBTransientVector<'T * 'T>.MkEmptyWithToken((vec1 :?> RRBTransientVector<'T>).Owner)
+            else RRBTransientVector<'T * 'T>.MkEmpty()
         for item1, item2 in Seq.zip vec1 vec2  do
             if pred item1 item2 then transient <- transient.Push (item1, item2) :?> RRBTransientVector<'T * 'T>
-        transient.Persistent() :> RRBVector<'T * 'T>
+        if resultShouldBeTransient then transient :> RRBVector<_> else transient.Persistent() :> RRBVector<_>
+
     let filteri2 pred (vec1 : RRBVector<'T>) (vec2 : RRBVector<'T>) =
-        let mutable transient = RRBTransientVector<'T * 'T>.MkEmpty()
+        let resultShouldBeTransient = vec1 |> isTransient && vec2 |> isTransient && isSameObj (vec1 :?> RRBTransientVector<'T>).Owner (vec2 :?> RRBTransientVector<'T>).Owner
+        let mutable transient =
+            if resultShouldBeTransient
+            then RRBTransientVector<'T * 'T>.MkEmptyWithToken((vec1 :?> RRBTransientVector<'T>).Owner)
+            else RRBTransientVector<'T * 'T>.MkEmpty()
         let mutable i = 0
         for item1, item2 in Seq.zip vec1 vec2  do
             if pred i item1 item2 then transient <- transient.Push (item1, item2) :?> RRBTransientVector<'T * 'T>
             i <- i + 1
-        transient.Persistent() :> RRBVector<'T * 'T>
+        if resultShouldBeTransient then transient :> RRBVector<_> else transient.Persistent() :> RRBVector<_>
+
     let inline find f (vec : RRBVector<'T>) = vec |> Seq.find f
     let inline findBack f (vec : RRBVector<'T>) = vec.RevIterItems() |> Seq.find f
     let inline findIndex f (vec : RRBVector<'T>) = vec |> Seq.findIndex f
@@ -1102,29 +1188,38 @@ module RRBVector =
     let inline foldBack2 (initState : 'State) folder (vec1 : RRBVector<'T1>) (vec2 : RRBVector<'T2>) = (vec1.RevIterItems(), vec2.RevIterItems()) ||> Seq.fold2 (fun a b c -> folder b c a) initState
     let inline forall f (vec : RRBVector<'T>) = vec |> Seq.forall f
     let inline forall2 f (vec1 : RRBVector<'T1>) (vec2 : RRBVector<'T2>) = (vec1, vec2) ||> Seq.forall2 f
-    let inline groupBy f (vec : RRBVector<'T>) = vec |> Seq.groupBy f |> ofSeq
+
+    let groupBy f (vec : RRBVector<'T>) =
+        if vec |> isTransient then
+            let result = RRBTransientVector<_>.MkEmptyWithToken((vec :?> RRBTransientVector<'T>).Owner)
+            for resultItem in vec |> Seq.groupBy f do
+                result.Push resultItem |> ignore
+            result :> RRBVector<_>
+        else
+            vec |> Seq.groupBy f |> ofSeq
+
     let head (vec : RRBVector<'T>) =
         if vec.Length = 0 then invalidArg "vec" "Can't get head of empty vector"
         vec.[0]
 
     let indexed (vec : RRBVector<'T>) =
-        // TODO: Benchmark the ofSeq version vs. the "unrolled" one below
-        vec |> Seq.indexed |> ofSeq
-
-        // "Unrolled" version, which may or may not be faster
-        // let mutable transient = RRBTransientVector.MkEmpty<int * 'T>()
-        // let mutable i = 0
-        // for item in vec do
-        //     transient <- transient.Push (i, item)
-        //     i <- i + 1
-        // transient.Persistent() :> RRBVector<'T>
+        let mutable transient =
+            if vec |> isTransient
+            then RRBTransientVector<int * 'T>.MkEmptyWithToken((vec :?> RRBTransientVector<'T>).Owner)
+            else RRBTransientVector<int * 'T>.MkEmpty()
+        let mutable i = 0
+        for item in vec do
+            transient.Push (i, item) |> ignore
+            i <- i + 1
+        if vec |> isTransient then
+            transient :> RRBVector<_>
+        else
+            transient.Persistent() :> RRBVector<_>
 
     //  vec |> Seq.indexed |> RRBHelpers.buildTreeOfSeqWithKnownSize (ref null) vec.Length
     let inline init size f = Seq.init size f |> ofSeq
     let inline isEmpty (vec : RRBVector<'T>) = vec.IsEmpty()
-    // Marking the `item` function as "inline" gets error FS1114: The value 'Ficus.RRBVector.RRBVectorModule.item' was marked inline but was not bound in the optimization environment
-    // What does that mean?
-    let item idx (vec : RRBVector<'T>) = vec.[idx]
+    let inline item idx (vec : RRBVector<'T>) = vec.[idx]
     let inline iter f (vec : RRBVector<'T>) = vec |> Seq.iter f
     let inline iter2 f (vec1 : RRBVector<'T1>) (vec2 : RRBVector<'T2>) = (vec1, vec2) ||> Seq.iter2 f
     let inline iteri f (vec : RRBVector<'T>) = vec |> Seq.iteri f
@@ -1135,63 +1230,172 @@ module RRBVector =
     let inline length (vec : RRBVector<'T>) = vec.Length
     // TODO: Make map family of functions use IterEditableLeaves when vector is transient (see FIXME below)
     // TODO: Go through the functions and find any that make the transient be the same size, or just a little larger (e.g. scan), and use IterEditableLeaves there too (with one Insert for scan)
-    let inline map f (vec : RRBVector<'T>) = Seq.map f vec |> ofSeq  // FIXME: This needs to be "smarter" if dealing with transient trees, since we need to maintain owner tokens
-    let inline map2 f (vec1 : RRBVector<'T1>) (vec2 : RRBVector<'T2>) = Seq.map2 f vec1 vec2 |> ofSeq
-    let inline map3 f (vec1 : RRBVector<'T1>) (vec2 : RRBVector<'T2>) (vec3 : RRBVector<'T3>) = Seq.map3 f vec1 vec2 vec3 |> ofSeq
-    let inline mapi f (vec : RRBVector<'T>) = Seq.mapi f vec |> ofSeq
-    let inline mapi2 f (vec1 : RRBVector<'T1>) (vec2 : RRBVector<'T2>) = Seq.mapi2 f vec1 vec2 |> ofSeq
+
+
+    let map f (vec : RRBVector<'T>) =
+        if vec |> isTransient then
+            let result = RRBTransientVector<_>.MkEmptyWithToken((vec :?> RRBTransientVector<'T>).Owner)
+            for item in vec do
+                result.Push (f item) |> ignore
+            result :> RRBVector<_>
+        else
+            vec |> Seq.map f |> ofSeq
+            // TODO: Benchmark the Seq.map version (the else block here) and see if it would be faster to use the same "unrolled" version we use for transients
+
+    let map2 f (vec1 : RRBVector<'T1>) (vec2 : RRBVector<'T2>) =
+        let resultShouldBeTransient = vec1 |> isTransient && vec2 |> isTransient && isSameObj (vec1 :?> RRBTransientVector<'T1>).Owner (vec2 :?> RRBTransientVector<'T2>).Owner
+        if resultShouldBeTransient then
+            let result = RRBTransientVector<_>.MkEmptyWithToken((vec1 :?> RRBTransientVector<'T1>).Owner)
+            use iter1 = vec1.IterItems().GetEnumerator()
+            use iter2 = vec2.IterItems().GetEnumerator()
+            while iter1.MoveNext() && iter2.MoveNext() do
+                result.Push (f iter1.Current iter2.Current) |> ignore
+            result :> RRBVector<_>
+        else
+            Seq.map2 f vec1 vec2 |> ofSeq
+            // TODO: Ditto re: benchmark for Seq.map
+
+    let map3 f (vec1 : RRBVector<'T1>) (vec2 : RRBVector<'T2>) (vec3 : RRBVector<'T3>) =
+        let resultShouldBeTransient = vec1 |> isTransient && vec2 |> isTransient && vec3 |> isTransient
+                                      && isSameObj (vec1 :?> RRBTransientVector<'T1>).Owner (vec2 :?> RRBTransientVector<'T2>).Owner
+                                      && isSameObj (vec2 :?> RRBTransientVector<'T2>).Owner (vec3 :?> RRBTransientVector<'T3>).Owner
+        if resultShouldBeTransient then
+            let result = RRBTransientVector<_>.MkEmptyWithToken((vec1 :?> RRBTransientVector<'T1>).Owner)
+            use iter1 = vec1.IterItems().GetEnumerator()
+            use iter2 = vec2.IterItems().GetEnumerator()
+            use iter3 = vec3.IterItems().GetEnumerator()
+            while iter1.MoveNext() && iter2.MoveNext() && iter3.MoveNext() do
+                result.Push (f iter1.Current iter2.Current iter3.Current) |> ignore
+            result :> RRBVector<_>
+        else
+            Seq.map3 f vec1 vec2 vec3 |> ofSeq
+            // TODO: Ditto re: benchmark for Seq.map
+
+    let mapi f (vec : RRBVector<'T>) =
+        if vec |> isTransient then
+            let result = RRBTransientVector<_>.MkEmptyWithToken((vec :?> RRBTransientVector<'T>).Owner)
+            let mutable i = 0
+            for item in vec do
+                result.Push (f i item) |> ignore
+                i <- i + 1
+            result :> RRBVector<_>
+        else
+            vec |> Seq.mapi f |> ofSeq
+            // TODO: Ditto re: benchmark for Seq.map
+
+    let mapi2 f (vec1 : RRBVector<'T1>) (vec2 : RRBVector<'T2>) =
+        let resultShouldBeTransient = vec1 |> isTransient && vec2 |> isTransient && isSameObj (vec1 :?> RRBTransientVector<'T1>).Owner (vec2 :?> RRBTransientVector<'T2>).Owner
+        if resultShouldBeTransient then
+            let result = RRBTransientVector<_>.MkEmptyWithToken((vec1 :?> RRBTransientVector<'T1>).Owner)
+            let mutable i = 0
+            use iter1 = vec1.IterItems().GetEnumerator()
+            use iter2 = vec2.IterItems().GetEnumerator()
+            while iter1.MoveNext() && iter2.MoveNext() do
+                result.Push (f i iter1.Current iter2.Current) |> ignore
+                i <- i + 1
+            result :> RRBVector<_>
+        else
+            Seq.mapi2 f vec1 vec2 |> ofSeq
+            // TODO: Ditto re: benchmark for Seq.map
 
     let mapFold folder initState (vec : RRBVector<'T>) =
-        if isEmpty vec then empty<'T> else
-        let mutable transient = RRBTransientVector<'T>.MkEmpty()
+        if isEmpty vec then vec else
+        let resultShouldBeTransient = vec |> isTransient
+        let mutable transient =
+            if resultShouldBeTransient
+            then RRBTransientVector<'T>.MkEmptyWithToken((vec :?> RRBTransientVector<'T>).Owner)
+            else RRBTransientVector<'T>.MkEmpty()
         let mutable state = initState
         for item in vec do
             let item',state' = folder state item
-            transient <- transient.Push item' :?> RRBTransientVector<'T>
+            transient.Push item' |> ignore
             state <- state'
-        transient.Persistent() :> RRBVector<'T>
+        if resultShouldBeTransient then transient :> RRBVector<_> else transient.Persistent() :> RRBVector<_>
 
     let mapFoldBack folder (vec : RRBVector<'T>) initState =
-        if isEmpty vec then empty<'T> else
-        let mutable transient = RRBTransientVector<'T>.MkEmpty()
+        if isEmpty vec then vec else
+        let resultShouldBeTransient = vec |> isTransient
+        let mutable transient =
+            if resultShouldBeTransient
+            then RRBTransientVector<'T>.MkEmptyWithToken((vec :?> RRBTransientVector<'T>).Owner)
+            else RRBTransientVector<'T>.MkEmpty()
         let mutable state = initState
         for item in vec.RevIterItems() do
             let item',state' = folder item state
             transient <- transient.Push item' :?> RRBTransientVector<'T>
             state <- state'
-        transient.Persistent() :> RRBVector<'T>
+        if resultShouldBeTransient then transient :> RRBVector<_> else transient.Persistent() :> RRBVector<_>
 
     let inline max (vec : RRBVector<'T>) = vec |> Seq.max
     let inline maxBy f (vec : RRBVector<'T>) = vec |> Seq.maxBy f
     let inline min (vec : RRBVector<'T>) = vec |> Seq.min
     let inline minBy f (vec : RRBVector<'T>) = vec |> Seq.minBy f
-    let inline pairwise (vec : RRBVector<'T>) = vec |> Seq.pairwise |> ofSeq
+
+    let pairwise (vec : RRBVector<'T>) =
+        if vec |> isTransient then
+            let result = RRBTransientVector<_>.MkEmptyWithToken((vec :?> RRBTransientVector<'T>).Owner)
+            use iter1 = vec.IterItems().GetEnumerator()
+            use iter2 = vec.IterItems().GetEnumerator()
+            if not (iter2.MoveNext()) then
+                // Input vector was empty
+                result :> RRBVector<_>
+            else
+                while iter1.MoveNext() && iter2.MoveNext() do
+                    result.Push (iter1.Current, iter2.Current) |> ignore
+                result :> RRBVector<_>
+        else
+            vec |> Seq.pairwise |> ofSeq
+            // TODO: Ditto re: benchmark for Seq.map
+
     let partition pred (vec : RRBVector<'T>) =
-        let mutable trueItems = RRBTransientVector<'T>.MkEmpty()
-        let mutable falseItems = RRBTransientVector<'T>.MkEmpty()
+        let resultShouldBeTransient = vec |> isTransient
+        let mutable trueItems =
+            if resultShouldBeTransient
+            then RRBTransientVector<'T>.MkEmptyWithToken((vec :?> RRBTransientVector<'T>).Owner)
+            else RRBTransientVector<'T>.MkEmpty()
+        let mutable falseItems =
+            if resultShouldBeTransient
+            then RRBTransientVector<'T>.MkEmptyWithToken((vec :?> RRBTransientVector<'T>).Owner)
+            else RRBTransientVector<'T>.MkEmpty()
         for item in vec do
             if pred item then trueItems <- trueItems.Push item :?> RRBTransientVector<'T> else falseItems <- falseItems.Push item :?> RRBTransientVector<'T>
-        trueItems.Persistent() :> RRBVector<'T>, falseItems.Persistent() :> RRBVector<'T>
+        if resultShouldBeTransient then
+            trueItems :> RRBVector<'T>, falseItems :> RRBVector<'T>
+        else
+            trueItems.Persistent() :> RRBVector<'T>, falseItems.Persistent() :> RRBVector<'T>
 
     let permute f (vec : RRBVector<'T>) = // TODO: Implement a better version once we have transient RRBVectors, so we don't have to build an intermediate array
         let arr = Array.zeroCreate vec.Length
+        let seen = Array.zeroCreate vec.Length
         let items = (vec :> System.Collections.Generic.IEnumerable<'T>).GetEnumerator()
         let mutable i = 0
         while items.MoveNext() do
-            arr.[f i] <- items.Current
+            let newIdx = f i
+            arr.[newIdx] <- items.Current
+            seen.[newIdx] <- 1uy
             i <- i + 1
-        arr |> ofArray
+        for i = 0 to seen.Length - 1 do
+            if seen.[i] <> 1uy then invalidArg "f" "The function did not compute a permutation."
+        if vec |> isTransient then
+            // Now mutate the transient in-place
+            for i = 0 to arr.Length - 1 do
+                vec.Update i arr.[i] |> ignore
+            vec :> RRBVector<_>
+        else
+            arr |> ofArray
 
     let inline pick f (vec : RRBVector<'T>) = vec |> Seq.pick f
     let inline reduce f (vec : RRBVector<'T>) = vec |> Seq.reduce f
     let reduceBack f (vec : RRBVector<'T>) = let f' = flip f in vec.RevIterItems() |> Seq.reduce f'
-    let replicate count value = // TODO: Implement this better once we have transient RRBVectors (or once we can do updates on transient PersistentVectors)
+
+    let replicate count value =
         if count = 0 then empty<'T> else
         let mutable transient = RRBTransientVector<'T>.MkEmpty()
         for i = 1 to count do
             transient <- transient.Push value :?> RRBTransientVector<'T>
         transient.Persistent() :> RRBVector<'T>
 
+// NOTE: Converted code up to this point to be transient-aware. TODO: Convert code below to be more efficient with transients, and preserve owner tokens when possible.
     let rev (vec : RRBVector<'T>) =
         if isEmpty vec then empty<'T> else
         let mutable transient = RRBTransientVector<'T>.MkEmpty()