Draw a pretty UTF-8 box around some text in Tcl

box.tcl

# Draw a UTF-8 box around some text. Useful for pretty-printing, logging, etc.
#
# @param str String to draw box around
# @return String enclosed in a fancy box
proc box str {
    # Draw the top of the box
    #
    # @param length Number representing how long the top should be
    # @return String drawing the top of the box
    proc top length {
       append result "┌"

       # We add two here to keep the formatting evenly spaced
       incr length +2

       while {$length > 0} {
           append result "─"

           incr length -1
       }

       append result "┐\n"

       return $result
    }

    # Draw the bottom of the box
    #
    # @param length Number representing how long the bottom should be
    # @return String drawing the bottom of the box
    proc bottom length {
       append result "└"

       # We add two here to keep the formatting evenly spaced
       incr length +2

       while {$length > 0} {
           append result "─"

           incr length -1
       }

       append result "┘\n"

       return $result
    }

    set lines   [split [string trim $str] \n]
    set lengths [lmap line $lines {string length $line}]
    set longest [lindex [lsort -real $lengths] end]

    # Now we are loop through and format the "inside" of the box.

    append result [top $longest]

    foreach line $lines {
        set length    [string length $line]
        set remaining [expr $longest - $length + 1]

        append result "│ $line"

        while {$remaining > 0} {
          append result " "

          incr remaining -1
        }

        append result "│\n"
    }

    append result [bottom $longest]

    return $result
}