gistfile1.tcl

proc addcomma {num} {
    set s {}; set r {}
    if {$num < 0} {
        set result "-"
        set num [expr abs($num)]
    }
    lassign [split $num .] upper lower
    set len [string length $upper]
    for {set i 0} {$i < $len} {incr i} {
        set s [list [string index $upper $i] $s]
    }
    for {set i 1} {$i <= $len} {incr i} {
        lassign $s top s
        set r [list $top $r]
        if { [llength $s] && ![expr {$i % 3}] } { set r [list "," $r] }
    }
    while {[llength $r]} { lassign $r top r; append result $top }
    if {$lower ne {}} { append result "." $lower }
    return $result
}