Property Encapsulation

atom

An atom is a single non-white space sequence. Colours and dimensions are usually created as atoms.

-background red
-foreground #fff
            

Curly braces, {}

Curly braces enclose either strings or lists. The contents of such a property is taken as is and does not get evaluated. Curly braces are for Option Database entries and also for Message Catalog data. In case of Message Catalog entries: A call to »mc« is placed before the string.

-text {This is a text string}
-command {
    ThisIsAScript evaluated;
    WheneverTheCommand EventHandler;
    OfTheControlInQuestionIsBeing triggered;
}
...

# Option Database with curly braces and »mc«:
option add *MyTemplate.label.text \
   {ODB String value}

# The message catalog is feed into
# the option database.
option add *MyTemplate.label_2.text \
   [mc {ODB String value}]

list, subst

The two remaining forms are related to command scripts. »list« is the preferred form. »list« is context free, whereas »subst« is not.

Jeszra has to resort to subst for consecutive commands. Such as an additional »break« inside an event binding. It is safer to use single commands and thus avoiding »subst«.

-command [list doSomethingWith $base]

...
# Here subst is unavoidable:
bind $base$w(1) <1> [subst {
     doSomethingWith $base$w(2);
     break;
}]


...
# Better use an event wrapper returning break.
proc eventBreakDoSomethingWith window {
  doSomethingWith $window;
  return -break
}
bind $base$w(1) <1> \
   [list eventBreakDoSomethingWith $base$w(2)]

Jeszra tries to avoid both forms. »list« and »subst« are usually used for variable substitutions. Typical situations are references to window path names –as seen in the code fragment above– through variables ($base, $base$w(n)).

Variable substitutions are auto-generated by Jeszra. The variable substitution occurs for every window path name used inside of a command property or event handler.

.my.window ➟  $base$w(1)
.my ➟  $base$w(0)
.window := contents of template 
           variable »w« with index 1.