initialize
   super initialize.
   shapes := Accumulator new.

 save
   shapes set: (shape set: dim).
   self inform: shapes printAsText.

 renderContentOn: html
   |group|
   html heading level: 1; with: 'Calculate Shape properties'.
   html form: [
     group := html radioGroup.
     group radioButton
       callback: [ shape := Sphere new];
       selected: true.
     html text: 'Sphere'.
     group radioButton
       callback: [ shape := Cube new ].
     html text: 'Cube'.
     html textInput
       callback: [ :value | dim := value];
        value: 0.
      html submitButton on: #save of: self.
 ]