proc bubble_sort {a} {
   if {[llength $a] >= 2} {
     for {set i [expr [llength $a]-1]} {$i > 0} {incr i -1} {
       set has_swapped "FALSE"
       for {set j 0} {$j < $i} {incr j} {
         if {[lindex $a $j] > [lindex $a [expr $j + 1]]} {
           set temp [lindex $a $j]
           set a [lreplace $a $j $j [lindex $a [expr $j + 1]]]
           set a [lreplace $a [expr $j + 1] [expr $j + 1] $temp]
           set has_swapped "TRUE"
         }
       }
       if {$has_swapped == "FALSE"} {
         break
       }
     }
   }
   return $a
 }

package require Tcl 8.5
package require struct::list
 
proc bubblesort {A} {
    set len [llength $A]
    set swapped true
    while {$swapped} {
        set swapped false
        for {set i 0} {$i < $len - 1} {incr i} {
            set j [expr {$i + 1}]
            if {[lindex $A $i] > [lindex $A $j]} {
                struct::list swap A $i $j
                set swapped true
            }
        }
        incr len -1
    }
    return $A
}
 
puts [bubblesort {8 6 4 2 1 3 5 7 9}] ;# => 1 2 3 4 5 6 7 8 9