Changes since 1.0:

Changes since 1.0:
  - views now work with match.ss and signal errors if used outside match.
  - clarified documentation: more examples; clarified requirements on
    define-view's subforms; ditto for view's.
  - define-view now has guard to ensure that view-name is an identifier.
  - added error cases to define-view
  - fixed bug in define-view: it now evaluates each argument exactly once.