Writing a lazy, functional, interactive command line application in Clojure

Question

I'm wondering: what is the best way to write a Clojure program that interacts with a user or another program thorough stdin and stdout?

Clearly it would be possible to write some kind of imperative loop, but I'm hoping to find something more lazy / functional, a bit inspired by Haskell's "interact" function.

This is a surprisingly hard question. perhaps the community needs clojure.contrib.interact — Arthur Ulfeldt
– Arthur Ulfeldt, Commented Mar 31, 2011 at 18:42

dbyrne · Accepted Answer · 2011-04-05 19:08:54Z

5

This was the best I could come up with:

(defn interact [f]
  (lazy-seq 
    (cons (do (let [input (read-line)
                    result (f input)]
                (println result)
                {:input input :result result}))
          (interact f))))

You could use it like this:

(def session
  (take-while #(not= (:result %) 0)
              (interact count)))

REPL:

user=> (str "Total Length: " (reduce #(+ %1 (:result %2)) 0 session))
foobar
6
stackoverflow
13

0
"Total Length: 19"
user=> session
({:input "foobar", :result 6} {:input "stackoverflow", :result 13})

edited Apr 5, 2011 at 19:08

answered Apr 5, 2011 at 15:49

dbyrne

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