gistfile1.clj

(defn foo [x] (apply str x))

(ann foo [(U (Vector* String) 
             (Seq* String) 
             (List* String)) 
          -> String])


user> (cf (foo ["a" "b"]))
>> java.lang.String

user> (cf (foo (seq ["a" "b"])))


Exception Type Error, NO_SOURCE_FILE:1

Actual type
	(clojure.core.typed/Option (I (clojure.lang.ISeq (U (Value "a") (Value "b"))) (CountRange 1)))
is not a subtype of Expected type
	(U [java.lang.String] (Seq* java.lang.String) (List* java.lang.String))  clojure.core.typed/type-error (subtype.clj:24)

user> (cf (foo (list "a" "b")))


Exception Type Error, NO_SOURCE_FILE:1

Actual type
	(clojure.lang.PersistentList (U (Value "a") (Value "b")))
is not a subtype of Expected type
	(U [java.lang.String] (Seq* java.lang.String) (List* java.lang.String))  clojure.core.typed/type-error (subtype.clj:24)


;; My goal was to define a TFn as follows 


(t/def-alias Sequential* (TFn [[x :variance :covariant]]
                              (U (Vector* x)
                                 (List* x)
                                 (Seq* x))))
;; I tried getting inspiration from https://github.com/clojure/core.typed/blob/master/src/main/clojure/clojure/core/typed/ann.clj 

;; From what I can see maybe Seqable is what I should be doing instead of all that. But I couldn't get it to work/load
(ann foo [(Seqable String)  -> String])
Exception Cannot parse list: (Seqable String)  clojure.core.typed/eval10041/fn--10043 (parse.clj:363)

;; adding ISeq to my crazy (and likely wrong) Sequantial* did the trick for (seq [..]) but it still not perfect.