if 0 {[Richard Suchenwirth] 2003-08-12 - In contrast to [a basic editor] which has quite some features, here's an utterly simple one which just allows to load and save files, and of course edit, and cut and paste, and whatever is built-in into the [text] widget anyway. And it has a bit "online help"... ;-)

This is yet another study in [literate programming]. For the bare source code (26 lines), see [A minimal editor].

It is always a good idea to start a source file with some explanations on the name, purpose, author, and date. I have recently picked up the habit to put this information into a string variable (which in Tcl can easily span multiple lines), so the same info is presented to the reader of the source code, and can be displayed as online help:
}
 set about "minEd - a minimal editor
 Richard Suchenwirth 2003
 F1: help
 F2: load
 F3: save
 "
if 0 {The visible part of Graphical User Interfaces consists of [widgets]. For this editor, I of course need a [text] widget, and a vertical [scrollbar]. With the option "-wrap word" for the text widget, another horizontal scrollbar is not needed - lines longer than the window just wrap at word boundaries.

Although the scrollbar comes to the right of the text, I create and [pack] it first. The reason is that when a window is made smaller by the user, the widgets last packed first lose visibility.

These two lines also illustrate the coupling between a scrollbar and the widget it controls
}
 pack [scrollbar .y -command ".t yview"] -side right -fill y
 pack [text .t -wrap word -yscrollc ".y set"] -side right -fill both -expand 1

 bind . <F1> {tk_messageBox -message $about}
 bind . <F2> {loadText .t [tk_getOpenFile]}
 bind . <F3> {saveText .t [tk_getSaveFile]}

 if {$argv != ""} {loadText .t [lindex $argv 0]}

 proc loadText {w fn} {
    if {$fn==""} return
    wm title . [file tail $fn]
    set fp [open $fn]
    $w delete 1.0 end
    $w insert end [read $fp]
    close $fp
 }
 proc saveText {w fn} {
    if {$fn==""} return
    set fp [open $fn w]
    puts -nonewline $fp [$w get 1.0 "end - 1 c"]
    close $fp
 }

if 0 {[DKF]: Are you targetting 8.4 or later?  If so, add ''-undo 1'' to the options to [text] and get full undo/redo support. Easy!}
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[Arts and crafts of Tcl-Tk programming]