(examples-for len

("nonzero"       (len "foo-bar")  7)
("zero"          (len "")         0)
("nil is zero"   (len nil)        0)
("sym is nil"    (len 'abc)       nil)
("fn is nil"     (len len)        nil)
("number is nil" (len 234)        nil)

("ignores backslash-escaped interpolation symbol"  (len "hello \~world")  12)
("returns length of proper list"                   (len '(a b))            2)
("counts last item of  improper list"              (len '(a b c . d))      4)
("counts keys of empty hash"                       (len { })               0)

("counts keys of hash"
 (len { a 11 b 22 c 23 d nil e { nested t counted nil } })
 5))