(use gauche.collection) (use gauche.mop.singleton) (define-class <zero-collection-meta> (<singleton-meta>) ()) (define-class <zero-collection> (<collection>) () :metaclass <zero-collection-meta>) (define-method call-with-iterator ((class <zero-collection>) proc :key start) (proc (^ () #t) (^ () (err…</zero-collection></zero-collection-meta></collection></zero-collection></singleton-meta></zero-collection-meta>