Question

I want to create a Clojure macro that can read a file, when the file is read successfully the stream should be closed.

(import '(java.io FileReader File))

(defmacro read([x y]
`(let ~x 
  (try ~y 
   (. x close)
    (catch Exception e# e#))))) 

Called like this,

(read [stream (java.io.FileReader (java.io.File "somefile.txt"))] (. stream read)))

Results in this error

java.lang.Exception: No such var: user/x (NO_SOURCE_FILE:8) 

Does anyone have any suggestions, thanks.

Answer 1

Aren’t you looking for with-open, unless there is some reason that you want to explicitly use a macro?

(defn read [file-name]
  (with-open [reader (BufferedReader. (FileReader. file-name))]
    (doseq [line (line-seq reader)] (println line))))

According to the ClojureDocs page, it ensures that the reader is closed at the end of the form.

Hopefully that helps!