(define-syntax CaseMettaHelper
  (syntax-rules (else)
    ((_ else bi) (list else bi))
    ((_ ai bi) (list (list ai) bi))))

(define-syntax CaseMetta
  (syntax-rules (else)
    ((_ var ((pat body ...) ...))
     (case var (CaseMettaHelper pat body ...) ...))))


(display (CaseMetta 3 ((1 2) (else 4))))
;bad argument type - not a list: CaseMettaHelper356