         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 )

    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 = [

! Based on Clojure's PersistentVector by Rich Hickey.

USING: math accessors kernel sequences.private sequences arrays
combinators parser prettyprint.backend ;
IN: persistent-vectors

ERROR: empty-error pvec ;
