Recur not at tail position - recursion

Question

How can I use something similiar to recurnot at tail position?
Take a look at my code:
(defn -main [& args]
(println "Hi! Type a file name...")
(defn readFile[])
(let [fileName(read-line)]
(let [rdr (reader fileName)]
(if-not (.exists rdr)
((println "Sorry, this file doesn't exists. Type a valid file name...")
(recur)))
(defn list '())
(doseq [line (line-seq rdr)]
(if-not (= "" line)
(concat list '(line)))
(list))))
(defn fileLinesList (readFile))
...
...)
I know I can't use recur here... But I neither know how can I make it in clojure.
I'm a newbie in Clojure and I'm coming from a OOP context. So...
Is there a way to use recursion in this case?
What would be an alternative?

Answer 1

First of all you should not nest your functions definitions in another defn (-main in this case). defn or def always defines symbol bindings at the top level of namespace and they don't nest. If you want to define a locally scoped function you need to use let and fn, e.g.
(let [my-fn (fn [a b] (+ a b))]
(my-fn 1 2))
In your particular case I think it would be easier to split your code into multiple functions. This way it will be more readable.
Prompting for a file name is one piece of your logic.
(defn get-existing-filename []
(let [filename (read-line)]
(if (.exists (java.io.File. filename))
filename
(do
(println "Sorry, this file doesn't exists. Type a valid file name...")
(recur)))))
Then you can use it to read a file removing empty lines:
(with-open [input (clojure.java.io/reader (get-existing-filename))]
(->> (line-seq input)
(remove empty?)
(doall)))
For a file with following content:
AAA
BBB
CCC
DDD
it will return
("AAA" "BBB" "CCC" "DDD")
If you really want it as a single function, the following will work:
(defn read-file []
(let [filename (read-line)]
(if (.exists (java.io.File. filename))
(with-open [input (clojure.java.io/reader (get-existing-filename))]
(->> (line-seq input)
(remove empty?)
(doall)))
(do
(println "Sorry, this file doesn't exists. Type a valid file name...")
(recur)))))
Finally, this function can be called from -main.
I have also noticed another issue in your sample code:
((println "Sorry, this file doesn't exists. Type a valid file name...")
(recur))
if and if-not require a single expression for their then and else branches. If you want to have multiple expressions you need to nest them in do:
(do
(println "Sorry, this file doesn't exists. Type a valid file name...")
(recur))
If you need if or if-not without the else branch then you can use when or when-not macros. Then you don't need to wrap multiple expressions because when/when-not will wrap them for your inside of do.
(when true
(println 1)
(println 2))
is equivalent to
(if true
(do
(println 1)
(println 2)))