USING: math.ranges kernel random ;

: switch ( to from seq -- )
    3dup swap [ nth ] dip [ [ move ] keep ] 2dip rot set-nth ;

: randomize ( seq -- seq' )
    dup length 1-
    [ dup 1 > ] [
        [ [0,b) random ] keep dup 
        [ rot [ switch ] keep ] dip 1-
    ] [ drop ] while ;