[dbohdan] 2015-03-25: The following code is a [Tk] [spreadsheet] inspired, title included, by http://jsfiddle.net/ondras/hYfN3/. Halfway through writing it I found the [tiny spreadsheet] and lifted the idea of tracing variable reads to trigger recalculation from it. One important difference from the tiny spreadsheet is that TEAIPTT does not require a Tcl [expr] patch.


**Feature comparison with the JavaScript version**

| ✓ Under 30 lines of plain Tcl/Tk (rather than 30 lines of vanilla JS*) |
| ✓ Libraries used: none |
| ✓ [Excel]-like syntax (formulas start with "=") |
| ✓ Support for arbitrary expressions (=A1+B2*C3) |
| ✓ Circular reference prevention |
| ✗ Automatic persistence |

* Lines are assumed to be up to 100 characters long (because the under-30-line JavaScript spreadsheet uses lines longer than 80 characters, 100 is the next common limit and using lines of unlimited length would feel like cheating).

The smallest JS spreadsheet is currently this one: http://xem.github.io/sheet/ (227 bytes for the minimal version, 267b if we add automatic persistence).

**Screenshot**


[under-35-line-spreadsheet-screenshot]

**Code**


======
#!/usr/bin/wish
foreach row {0 1 2 3 4 5 6} {
    grid {*}[lmap {column} {"" A B C D E F} {
        set cell $column$row
        if {$column eq "" || $row == 0} {
            ::ttk::label .label$cell -text [expr {$row ? $row : $column}]
        } else {
            set ::formula($cell) [set ::$cell ""]
            trace add variable ::$cell read recalc
            ::ttk::entry .cell$cell -textvar ::$cell -width 10 -validate focus \
                    -validatecommand [list ::reveal-formula $cell %V %s]
        }
    }]
}
proc recalc {cell args} {
    catch {set ::$cell [uplevel #0 [list \
           expr [regsub -all {([A-F][1-6])} $::formula($cell) {$\1}]]]}
}
proc reveal-formula {cell event value} {
    if {$event eq "focusin"} {
        if {$::formula($cell) ne ""} { set ::$cell =$::formula($cell) }
        .cell$cell selection range 0 end
        .cell$cell icursor end
    } else { ;# focusout
        if {![regexp {^=(.*)} $value -> ::formula($cell)]} { set ::formula($cell) "" }
        foreach otherCell [array names ::formula] { recalc $otherCell }
    }
    return 1
}
======


**Discussion**


[AMG]: Exchanged the row and column [foreach] lines so that the tab key moves across rather than down.

[dbohdan] 2015-03-28: [xem], it is neat just how much functionality your spreadsheet packs in 0x00-0xE2 but it looks like it only recalculates formulas one step at a time. I.e., if you have A1 set to =B1 and B1 set to =C1 and then put the number 5 into C1 it will take ''two'' `onblur` events before the value propagates back to A1. This also means you can create stable infinite loops that will cycle values and `NaN`s between cells.

I wonder how much you could [code golf%|%golf] the Tcl/Tk version if you try to optimize for character count rather than line count and relax the requirement on `recalc`. Any takers? A page like [Golfed spreadsheet] would be appropriate for that. I also wonder what would be the minimal overhead of adding full recalculation with circular reference prevention to [xem]'s JS version.

[aspect] 2015-03-29: Fixed deletion of formulas and reduced by using [lmap], taking advantage of `-textvariable` to eliminate the `set-cell` proc and eliminating the test in `recalc` because [expr] will error on an empty expression.  Without `set-cell`, some explicit selection management is required on focusin, reducing the saving.  This might be improved with some careful event binding, rather than `-validate`.

<<categories>>Application | GUI | Spreadsheet