Lispy way to read user input from the keyboard in Clojure?

Question

I am writing a function for my Clojure program that reads user input from the keyboard. If the user enters invalid input, the user is warned and then prompted again. When using a procedural style in a language like Python, I would do something like this:

while 1:
    value = input("What is your decision?")
    if validated(value):
        break
    else:
        print "That is not valid."

The best I can come up with in Clojure is this:

(loop [value (do
               (println "What is your decision?")
               (read-line))]
  (if (validated value)
    value
    (recur (do
             (println "That is not valid.")
             (println "What is your decision?")
             (read-line)))))

This works, but it is redundant and seems verbose. Is there a more Lispy/Clojurey way to do this?

dnolen · Accepted Answer · 2010-11-23 03:27:54Z

21

(defn input []
   (println "What is your decision?")
   (if-let [v (valid? (read-line))]
      v
      (do
         (println "That is not valid")
         (recur)))

edited Nov 23, 2010 at 3:27

answered Nov 23, 2010 at 1:10

dnolen

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user61051 · Accepted Answer · 2010-11-23 19:13:42Z

8

Factor out the println/read-line combo into a get-line function:

(defn get-input [prompt]
  (println prompt)
  (read-line))

(defn get-validated-input []
  (loop [input (get-input "What is your decision?")]
    (if (valid? input)
      value
      (recur (get-input "That is not valid.\nWhat is your decision?")))))

This is basically what your Python version does; the difference is that get-input is built-in for Python.

answered Nov 23, 2010 at 19:13

user61051

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