Macro that transforms a DSL into a GUI.

The macro is a fairly simple substitution, it follows one of three patterns:

<Widget name>(arguments, for, widget, creator)[arguments, for, add, function]:
  <Children>

<Identifier>%<Widget name>(arguments, for, widget, creator)[arguments, for, add, function]:
  <Children>

%<Identifier>[arguments, for, add, function]:
  <Children>
"String"

Both ()-arguments and []-arguments can be omitted.

If the widget has no children the : must be omitted.

Identifiers create a var statement assigning the widget to the identifier, or assign the widget to the identifier if it already exists. Using %<identifier> you can add widget created previously, it takes the same add options and children as any other widget.

The string pattern is used for widgets which have an add function for string values, such as RadioButtons and ComboBox.

See genuiusg.nim for an example of usage.