diff --git a/extra/persistent-vectors/authors.txt b/extra/persistent-vectors/authors.txt
new file mode 100644
index 0000000000..1901f27a24
--- /dev/null
+++ b/extra/persistent-vectors/authors.txt
@@ -0,0 +1 @@
+Slava Pestov
diff --git a/extra/persistent-vectors/persistent-vectors-docs.factor b/extra/persistent-vectors/persistent-vectors-docs.factor
new file mode 100644
index 0000000000..b0cb512d43
--- /dev/null
+++ b/extra/persistent-vectors/persistent-vectors-docs.factor
@@ -0,0 +1,53 @@
+USING: help.markup help.syntax kernel math sequences ;
+IN: persistent-vectors
+
+HELP: new-nth
+{ $values { "val" object } { "i" integer } { "seq" sequence } }
+{ $contract "Persistent analogue of " { $link set-nth } ". Outputs a new sequence with the " { $snippet "i" } "th element replaced by " { $snippet "val" } "." }
+{ $notes "This operation runs in " { $snippet "O(log_32 n)" } " time on " { $link persistent-vector } " instances and " { $snippet "O(n)" } " time on all other sequences." } ;
+
+HELP: ppush
+{ $values { "val" object } { "i" integer } { "seq" sequence } }
+{ $contract "Persistent analogue of " { $link push } ". Outputs a new sequence with all elements of " { $snippet "seq" } " together with " { $snippet "val" } " added at the end." }
+{ $notes "This operation runs in amortized " { $snippet "O(1)" } " time on " { $link persistent-vector } " instances and " { $snippet "O(n)" } " time on all other sequences." } ;
+
+HELP: ppop
+{ $values { "val" object } { "i" integer } { "seq" sequence } }
+{ $contract "Persistent analogue of " { $link pop } ". Outputs a new sequence with all elements of " { $snippet "seq" } " except for the final element." }
+{ $notes "This operation runs in amortized " { $snippet "O(1)" } " time on " { $link persistent-vector } " instances and " { $snippet "O(n)" } " time on all other sequences." } ;
+
+HELP: PV{
+{ $syntax "elements... }" }
+{ $description "Parses a literal " { $link persistent-vector } "." } ;
+
+HELP: >persistent-vector
+{ $values { "seq" sequence } { "pvec" persistent-vector } }
+{ $description "Creates a " { $link persistent-vector } " with the same elements as " { $snippet "seq" } "." } ;
+
+HELP: persistent-vector
+{ $class-description "The class of persistent vectors." } ;
+
+HELP: pempty
+{ $values { "pvec" persistent-vector } }
+{ $description "Outputs an empty " { $link persistent-vector } "." } ;
+
+ARTICLE: "persistent-vectors" "Persistent vectors"
+"A " { $emphasis "persistent vector" } " differs from an ordinary vector (" { $link "vectors" } ") in that it is immutable, and all operations yield new persistent vectors instead of modifying inputs. Unlike immutable operations on ordinary sequences, persistent vector operations are efficient and run in sub-linear time."
+$nl
+"The class of persistent vectors:"
+{ $subsection persistent-vector }
+"Persistent vectors support the immutable sequence protocol, namely as " { $link length } " and " { $link nth } ", and so can be used with most sequence words (" { $link "sequences" } ")."
+$nl
+"In addition to standard sequence operations, persistent vectors implement efficient operations specific to them. They run in sub-linear time on persistent vectors, and degrate to linear-time algorithms on ordinary sequences:"
+{ $subsection new-nth }
+{ $subsection ppush }
+{ $subsection ppop }
+"The empty persistent vector, used for building up all other persistent vectors:"
+{ $subsection pempty }
+"Converting a sequence into a persistent vector:"
+{ $subsection >persistent-vector }
+"Persistent vectors have a literal syntax:"
+{ $subsection POSTPONE: PV{ }
+"This implementation of persistent vectors is based on the " { $snippet "clojure.lang.PersistentVector" } " class from Rich Hickey's Clojure language for the JVM (" { $url "http://clojure.org" } ")." ;
+
+ABOUT: "persistent-vectors"
diff --git a/extra/persistent-vectors/persistent-vectors-tests.factor b/extra/persistent-vectors/persistent-vectors-tests.factor
new file mode 100644
index 0000000000..f871c95e16
--- /dev/null
+++ b/extra/persistent-vectors/persistent-vectors-tests.factor
@@ -0,0 +1,63 @@
+IN: persistent-vectors.tests
+USING: tools.test persistent-vectors sequences kernel arrays
+random namespaces vectors math math.order ;
+
+\ new-nth must-infer
+\ ppush must-infer
+\ ppop must-infer
+
+[ 0 ] [ pempty length ] unit-test
+
+[ 1 ] [ 3 pempty ppush length ] unit-test
+
+[ 3 ] [ 3 pempty ppush first ] unit-test
+
+[ PV{ 3 1 3 3 7 } ] [
+    pempty { 3 1 3 3 7 } [ swap ppush ] each
+] unit-test
+
+[ { 3 1 3 3 7 } ] [
+    pempty { 3 1 3 3 7 } [ swap ppush ] each >array
+] unit-test
+
+{ 100 1060 2000 10000 100000 1000000 } [
+    [ t ] swap [ dup >persistent-vector sequence= ] curry unit-test
+] each
+
+[ ] [ 10000 [ drop 16 random-bits ] PV{ } map-as "1" set ] unit-test
+[ ] [ "1" get >vector "2" set ] unit-test
+
+[ t ] [
+    3000 [
+        drop
+        16 random-bits 10000 random
+        [ "1" [ new-nth ] change ]
+        [ "2" [ new-nth ] change ] 2bi
+        "1" get "2" get sequence=
+    ] all?
+] unit-test
+
+[ PV{ } ppop ] [ empty-error? ] must-fail-with
+
+[ t ] [ PV{ 3 } ppop empty? ] unit-test
+
+[ PV{ 3 7 } ] [ PV{ 3 7 6 } ppop ] unit-test
+
+[ PV{ 3 7 6 5 } ] [ 5 PV{ 3 7 6 } ppush ] unit-test
+
+[ ] [ PV{ } "1" set ] unit-test
+[ ] [ V{ } clone "2" set ] unit-test
+
+[ t ] [
+    100 [
+        drop
+        100 random [
+            16 random-bits [ "1" [ ppush ] change ] [ "2" get push ] bi
+        ] times
+        100 random "1" get length min [
+            "1" [ ppop ] change
+            "2" get pop*
+        ] times
+        "1" get "2" get sequence=
+    ] all?
+] unit-test
diff --git a/extra/persistent-vectors/persistent-vectors.factor b/extra/persistent-vectors/persistent-vectors.factor
new file mode 100644
index 0000000000..6ed43ca0af
--- /dev/null
+++ b/extra/persistent-vectors/persistent-vectors.factor
@@ -0,0 +1,185 @@
+! Based on Clojure's PersistentVector by Rich Hickey.
+
+USING: math accessors kernel sequences.private sequences arrays
+combinators parser prettyprint.backend fry debugger ;
+IN: persistent-vectors
+
+ERROR: empty-error pvec ;
+
+GENERIC: ppush ( obj seq -- seq' )
+
+M: sequence ppush swap suffix ;
+
+GENERIC: ppop ( seq -- seq' )
+
+M: sequence ppop 1 head* ;
+
+GENERIC: new-nth ( obj i seq -- seq' )
+
+M: sequence new-nth clone [ set-nth ] keep ;
+
+TUPLE: persistent-vector count root tail ;
+
+M: persistent-vector length count>> ;
+
+<PRIVATE
+
+TUPLE: node children level ;
+
+: node-mask HEX: 1f bitand ; inline
+
+: node-size 32 ; inline
+
+: tail-offset [ count>> ] [ tail>> children>> length ] bi - ;
+
+: node-shift -5 * shift ; inline
+
+: node-nth ( i node -- obj )
+    children>> [ node-mask ] dip nth ; inline
+
+: body-nth ( i node -- obj )
+    dup level>> 0 > [
+        [ drop ] [ [ level>> node-shift ] keep node-nth ] 2bi
+        body-nth
+    ] [
+        node-nth
+    ] if ; inline
+
+M: persistent-vector nth-unsafe
+    2dup tail-offset >=
+    [ tail>> node-nth ] [ root>> body-nth ] if ;
+
+: node-add ( obj node -- node' )
+    clone [ ppush ] change-children ;
+
+: ppush-tail ( obj pvec -- pvec' )
+    [ node-add ] change-tail ;
+
+: full? ( node -- ? )
+    children>> length node-size = ;
+
+: 1node ( obj level -- node )
+    node new
+        swap >>level
+        swap 1array >>children ;
+
+: 2node ( first second -- node )
+    2dup [ level>> ] bi@ assert=
+    [ 2array ] [ drop level>> 1+ ] 2bi node boa ;
+
+: new-child ( new-child node -- node' expansion/f )
+    dup full? [ tuck level>> 1node ] [ node-add f ] if ;
+
+: pset-last ( val seq -- seq' )
+    [ length 1- ] keep new-nth ;
+
+: node-set-last ( child node -- node' )
+    clone [ pset-last ] change-children ;
+
+: (ppush-new-tail) ( tail node -- node' expansion/f )
+    dup level>> 1 = [
+        new-child
+    ] [
+        tuck children>> peek (ppush-new-tail)
+        [ swap new-child ] [ swap node-set-last f ] ?if
+    ] if ;
+
+: do-expansion ( pvec root expansion/f -- pvec )
+    [ 2node ] when* >>root ;
+
+: ppush-new-tail ( obj pvec -- pvec' )
+    [ ] [ tail>> ] [ root>> ] tri
+    (ppush-new-tail) do-expansion
+    swap 0 1node >>tail ;
+
+M: persistent-vector ppush ( obj pvec -- pvec' )
+    clone
+    dup tail>> full?
+    [ ppush-new-tail ] [ ppush-tail ] if
+    [ 1+ ] change-count ;
+
+: node-set-nth ( val i node -- node' )
+    clone [ new-nth ] change-children ;
+
+: node-change-nth ( i node quot -- node' )
+    [ clone ] dip '[
+        clone [ , change-nth ] keep
+    ] change-children ; inline
+
+: (new-nth) ( val i node -- node' )
+    dup level>> 0 = [
+        [ node-mask ] dip node-set-nth
+    ] [
+        [ dupd level>> node-shift node-mask ] keep
+        [ (new-nth) ] node-change-nth
+    ] if ;
+
+M: persistent-vector new-nth ( obj i pvec -- pvec' )
+    2dup count>> = [ nip ppush ] [
+        clone
+        2dup tail-offset >= [
+            [ node-mask ] dip
+            [ node-set-nth ] change-tail
+        ] [
+            [ (new-nth) ] change-root
+        ] if
+    ] if ;
+
+: (ppop-contraction) ( node -- node' tail' )
+    clone [ unclip-last swap ] change-children swap ;
+
+: ppop-contraction ( node -- node' tail' )
+    [ (ppop-contraction) ] [ level>> 1 = ] bi swap and ;
+
+: (ppop-new-tail) ( root -- root' tail' )
+    dup level>> 1 > [
+        dup children>> peek (ppop-new-tail) over children>> empty?
+        [ 2drop ppop-contraction ] [ [ swap node-set-last ] dip ] if
+    ] [
+        ppop-contraction
+    ] if ;
+
+: ppop-tail ( pvec -- pvec' )
+    [ clone [ ppop ] change-children ] change-tail ;
+
+: ppop-new-tail ( pvec -- pvec' )
+    dup root>> (ppop-new-tail)
+    [
+        dup [ level>> 1 > ] [ children>> length 1 = ] bi and 
+        [ children>> first ] when
+    ] dip
+    [ >>root ] [ >>tail ] bi* ;
+
+PRIVATE>
+
+: pempty ( -- pvec )
+    T{ persistent-vector f 0 T{ node f { } 1 } T{ node f { } 0 } } ; inline
+
+M: persistent-vector ppop ( pvec -- pvec' )
+    dup count>> {
+        { 0 [ empty-error ] }
+        { 1 [ drop pempty ] }
+        [
+            [
+                clone
+                dup tail>> children>> length 1 >
+                [ ppop-tail ] [ ppop-new-tail ] if
+            ] dip 1- >>count
+        ]
+    } case ;
+
+M: persistent-vector like
+    drop pempty [ swap ppush ] reduce ;
+
+M: persistent-vector equal?
+    over persistent-vector? [ sequence= ] [ 2drop f ] if ;
+
+: >persistent-vector ( seq -- pvec ) pempty clone-like ; inline
+
+: PV{ \ } [ >persistent-vector ] parse-literal ; parsing
+
+M: persistent-vector pprint-delims drop \ PV{ \ } ;
+
+M: persistent-vector >pprint-sequence ;
+
+INSTANCE: persistent-vector immutable-sequence
diff --git a/extra/persistent-vectors/summary.txt b/extra/persistent-vectors/summary.txt
new file mode 100644
index 0000000000..19f3f66ca3
--- /dev/null
+++ b/extra/persistent-vectors/summary.txt
@@ -0,0 +1 @@
+Immutable vectors with O(log_32 n) random access and amortized O(1) push/pop
diff --git a/extra/persistent-vectors/tags.txt b/extra/persistent-vectors/tags.txt
new file mode 100644
index 0000000000..42d711b32b
--- /dev/null
+++ b/extra/persistent-vectors/tags.txt
@@ -0,0 +1 @@
+collections