Question

I’m using with-out-str to capture some data that is printed to stdout. Problem is that with-out-str seems to throw away the return value from my function. Is there any way I can capture both? I’d like to have my cake and eat it too.

Example:

(with-out-str (do (prn "test") (+ 1 1)))

Answer 1

Aping the definition of the core library’s with-out-str macro, you could define a similar one like this:

(defmacro with-out-str-and-value
  [& body]
  `(let [s# (new java.io.StringWriter)]
     (binding [*out* s#]
       (let [v# ~@body]
         (vector (str s#)
                 v#)))))

Without the values function from Common Lisp and its multiple function return values, here we return a vector instead; the first item is the text collected from standard output, and the second item is the value returned by evaluating the body form.