Comment 3 for bug 458164

another surprise found by Levente:

(typep (sb-pcl::class-prototype (class-of (lambda ()))) 'function) => T

but:

(defgeneric foo (f)
  (:method ((f function))
    (print 42)))

(foo (sb-pcl::class-prototype (class-of (lambda ())))) =>
"The value #<FUNCTION {10014238B1}> is not of type FUNCTION."

this is another argument to signal error in class-prototype for types that can not provide a prototype without surprises.