;; давайте подитожим

;; Returns true if x implements IPersistentCollection
(coll? [])                    ;; => true
(coll? (range 1))             ;; => true - (range ...) returns PersistentList or similar
(coll? 0)                     ;; => false
;; Achtung!
(coll? (to-array []))         ;; => false - (to-array coll) is Object[] but not instance of IPersistentCollection

;; If the collection is empty, returns nil.  (seq nil) returns nil.
;; ...works on Strings, native Java arrays and any objects that implement Iterable
(seq [])                      ;; => nil - falsy
(seq nil)                     ;; => nil - falsy
(seq (range 0))               ;; => nil - falsy
(seq (range 1))               ;; => (0) - truthy
;; Achtung!
(seq "ABC")                   ;; => (\A \B \C) - truthy
(seq 0)                       ;; throws IllegalArgumentException - java.lang.Long is not instance of ISeq

;; Return true if x implements ISeq
(seq? 0)                      ;; false
(seq? (range 0))              ;; true
(seq? [])                     ;; false
;; Achtung!
(seq? (seq []))               ;; false
(seq? (seq [nil]))            ;; true

;; Return true if the seq function is supported for x
(seqable? 0)                  ;; false
(seqable? (range 0))          ;; true
;; Achtung! empty colls are seqable
(seqable? [])                 ;; true
(seqable? #{})                ;; true
(seqable? {})                 ;; true
(seqable? "")                 ;; true

;; Returns true if coll implements Sequential
(sequential? [])              ;; true
(sequential? '())             ;; true
(sequential? (range 0))       ;; true
(sequential? 0)               ;; false
(sequential? nil)             ;; false
;; Achtung!
(sequential? #{})             ;; false - set is not Sequential
(sequential? {})              ;; false - map is not Sequential

(= '() [])                    ;; true