(Program
  (Case
    (Identifier)
    (When
      (Args
        (Identifier))
    {-(Identifier)-}
    {-(When
        (Args
          (Identifier))
        (Args
          (Identifier))
        (Else
          (Identifier)))-}))
{+(Case
    (When
      (Args
        (Boolean))
      (StringLiteral)))+})