Eskil

        # Four files, with optional revision
        set fields {base1 change1 base2 change2}
    
        ttk::label $win.l1 -text "Base 1"
        ttk::label $win.l2 -text "Changed 1"
        ttk::label $win.l3 -text "Base 2"
        ttk::label $win.l4 -text "Changed 2"
        set txt1 "First diff is made from Base 1 to Changed 1.\n If a file is\
                  empty and have a revision, the other file name is used."
        addBalloon $win.l1 $txt1
        addBalloon $win.l2 $txt1
        set txt2 [string map {1 2 First Second} $txt1]
        addBalloon $win.l3 $txt2
        addBalloon $win.l4 $txt2

        ttk::label $win.el -text "File path"
        ttk::label $win.rl -text "Rev"
        addBalloon $win.rl "If you want to use a revisioned controlled file\
                            instead\n of the one on disk, add a revision here.\
                            E.g. 0 can be used\n for latest commited revision."

        set n 0
        foreach field $fields {
            incr n
            ttk::entryX $win.e$n -width 60 -textvariable [myvar files($field)]
            ttk::button $win.b$n -text "Browse" \
                    -command [mymethod browseFile $field]
            ttk::entryX $win.r$n -width 6 -textvariable  [myvar revs($field)]
        }

        ttk::button $win.bd -text "Diff" -command [mymethod doFourWayDiff] \
                -underline 0 -width 8
        bind $win <Alt-d> [list $win.bd invoke]

        grid x       $win.el x       $win.rl -sticky w  -padx 3 -pady 3
        grid $win.l1 $win.e1 $win.b1 $win.r1 -sticky we -padx 3 -pady 3
        grid $win.l2 $win.e2 $win.b2 $win.r2 -sticky we -padx 3 -pady 3
        grid $win.l3 $win.e3 $win.b3 $win.r3 -sticky we -padx 3 -pady {10 3}
        grid $win.l4 $win.e4 $win.b4 $win.r4 -sticky we -padx 3 -pady 3

            set todo [list $field]
        }
        foreach fn $files field $todo {
            # Loop until any list ends
            if {$fn eq "" || $field eq ""} break
            # Sanity check
            if {[file exists $fn]} {
                set files($field) $fn
            }
        }
    }

    # Browse for file
    method browseFile {field} {
        set initDir [pwd]

        }
    }

    method doFourWayDiff {} {
        # Copy to local vars to be able to replace with defaults and parsed
        foreach field $fields {
            set filename($field) $files($field)
            set rev($field) [string trim $revs($field)]
        }
        # Fill in defaults, if only one file is given
        foreach {from to} $fields {
            if {$filename($to) eq ""} {
                set filename($to) $files($from)
            }
            if {$filename($from) eq ""} {
                set filename($from) $files($to)
            }
        }
        # Remember originals for display, they might be replaced below
        foreach field $fields {
            set origfile($field) $filename($field)
            set origrev($field)  $rev($field)
        }
        # Figure out any revisions
        foreach field $fields {
            # TODO: Move this to helper function in rev.tcl
            if {$rev($field) ne ""} {
                set revtype($field) [detectRevSystem $filename($field)]
                if {$revtype($field) eq ""} {
                    tk_messageBox -icon error -title "Eskil Error" \
                            -parent $win -message \
                            "Could not detect version system for file $filename($field)"
                    return
                    # TBD continue
                    set rev($field) ""
                    continue
                }
                set revList [list $rev($field)]
                set revList [eskil::rev::$revtype($field)::ParseRevs \
                                     $filename($field) $revList]
                if {[llength $revList] == 0} {
                    tk_messageBox -icon error -title "Eskil Error" \
                            -parent $win -message \
                            "Could not parse revision for file $filename($field)"
                    return
                    # TBD continue
                    set rev($field) ""
                } else {
                    set rev($field) [lindex $revList 0]
                }
            }
            # Still a revision?
            if {$rev($field) ne ""} {

        if {$::Pref(nocase)} {lappend opts -nocase}
        if {$::Pref(noempty)} {lappend opts -noempty}
        if {$::Pref(pivot) > 0} {lappend opts -pivot $::Pref(pivot)}

        # Do compare of files, to generate patches
        foreach side {1 2} {
            set differr [catch {DiffUtil::diffFiles {*}$opts \
                    $filename(base$side) $filename(change$side)} diffres]
            if {$differr != 0} {
                # TODO error
                return
            }
            set outfile($side) [tmpFile]
            set ch [open $outfile($side) w]
            foreach str {From To} field "base$side change$side" {

        }
 
        # Output diff
        for {set t 0} {$t < $n1} {incr t} {
            gets $ch1 apa
            puts $ch "- $apa"
            incr doingLine1
        }
        for {set t 0} {$t < $n2} {incr t} {
            gets $ch2 apa
            puts $ch "+ $apa"
            incr doingLine2
        }
    }
}

proc makeFourWayWin {} {
    set t 1
    set top .fourway$t
    while {[winfo exists $top]} {
        incr t
        set top .fourway$t
    }
    FourWay $top
}