I've been thinking about writing a very simple spreadsheet in tcl for a few weeks now.  It 
would store its data in [[array get]] format with cells named in the R1C1 style.  The main 
issue is that I wanted to '''much''' more flexable expr command.  I thought through various
preprocesing schemes to use before calling expr to evaluate the contents of a cell, then 
I found this handy patch[ http://www.elf.org/etc/tcl-expr-patch.html].  You eighter like this
or you don't.

Cell reference expansion is done with regsub, while the patched core allows procs to be used in
expr.


 array set Sheet {
        R1C1    { 3 }
        R1C2    { 5 + 4 }
        R1C3    R1C4
        R1C4    -6
        R1C5    { min(4, R1C3) }
        R1C6    { "TTText" }
        R2C7    { sum(R1C1:R1C2, 100, R1C1:R1C2, 5) }
 }

 proc min { a b } {
        return [expr $a < $b ? $a : $b]
 }

 proc sum { args } {
    return [substexpr [join [join $args] +]]
 }

 proc range { r1 c1 rn cn } {
        set list {}
        for { set r $r1 } { $r <= $rn } { incr r } {
        for { set c $c1 } { $c <= $cn } { incr c } {
                lappend list R${r}C${c}
        } }

        return $list
 }

 proc substexpr { cell } {
        global Cells

        regsub -all -- {R([0-9]+)C([0-9]+):R([0-9]+)C([0-9]+)} $cell    \
               {range(\1, \2, \3, \4)} code
        regsub -all -- {(R[0-9]+C[0-9]+)} $code {$Cells(\1)} code

        if { [catch { set result [expr $code] } reply] } { puts $reply }

        return $result
 }

 proc Sheet { name indx op } {
        global Sheet
        global Cells

        if { [catch { set val $Sheet($indx) } reply] } {
                set Cells($indx) 0
                return
        }
 }

 proc Cells { name indx op } {
        global Cells
        global Sheet

    if { ![catch { set val $Cells($indx) } reply] } {
        return
    }

    if { [catch { set Cells($indx) [substexpr $Sheet($indx)] }] } {
        set Cells($indx) 0
    }
 }

 array set Cells {}

 trace variable Cells r Cells
 trace variable Sheet r Sheet

 foreach cell [array names Sheet] {
        puts "$cell = $Cells($cell)"
 }