listTable.Widget.GTK should be record function

[AshleyYakeley]

• Requires Type variable quantification for record functions (and record constructors?) #312.

type Selector {-p,+q};

null.Selector: Selector {};

subtype WholeModel {-p,+q,+Entity} <: Selector {-p,+q};

listTable.Widget.GTK of
    type a;
    columns: List (WholeModel +Text *: (a -> WholeModel +Text));
    model: ListModel a;
    onActivate: a -> Action Any;
    selection: Selector a = null.Selector;
end: Widget.GTK;