Question

I’m trying to write a simple calculator with addition, subtraction, etc.

My problem is with getting the user input. How do I turn the string of numerical values into a vector? And also what is a better way to write the program?

(ns scalc.core)

(defn add
  [numbers]
  (println (apply + numbers)))

(defn numchoose
  []
  (println "What numbers?: ")
  (let [numbers (read-line)] numbers))

(defn opchoose
  []
  (println "What operation would you like to do?: ")
  (let [operation (read-line)]

    (if (= operation "add")
      (do
        (println "You chose to add.")
        (let [numvect (numchoose)]
              (add [numvect]))))))


(defn -main
  [& args]

  (opchoose)
  (numchoose))

And this is the error:

 ~/clj/scalc 1/7 % lein trampoline run -m scalc.core
What operation would you like to do?: 
add
You chose to add.
What numbers?: 
5 7
Exception in thread "main" java.lang.ClassCastException: Cannot cast java.lang.String to java.lang.Number
        at java.lang.Class.cast(Class.java:3005)
        at clojure.core$cast.invoke(core.clj:318)
        at clojure.core$_PLUS_.invoke(core.clj:927)
        at clojure.lang.AFn.applyToHelper(AFn.java:161)
        at clojure.lang.RestFn.applyTo(RestFn.java:132)
        at clojure.core$apply.invoke(core.clj:601)
        at scalc.core$add.invoke(core.clj:5)
        at scalc.core$opchoose.invoke(core.clj:21)
        at scalc.core$_main.doInvoke(core.clj:27)
        at clojure.lang.RestFn.invoke(RestFn.java:397)
        at clojure.lang.Var.invoke(Var.java:411)
        at user$eval15.invoke(NO_SOURCE_FILE:1)
        at clojure.lang.Compiler.eval(Compiler.java:6511)
        at clojure.lang.Compiler.eval(Compiler.java:6501)
        at clojure.lang.Compiler.eval(Compiler.java:6477)
        at clojure.core$eval.invoke(core.clj:2797)
        at clojure.main$eval_opt.invoke(main.clj:297)
        at clojure.main$initialize.invoke(main.clj:316)
        at clojure.main$null_opt.invoke(main.clj:349)
        at clojure.main$main.doInvoke(main.clj:427)
        at clojure.lang.RestFn.invoke(RestFn.java:421)
        at clojure.lang.Var.invoke(Var.java:419)
        at clojure.lang.AFn.applyToHelper(AFn.java:163)
        at clojure.lang.Var.applyTo(Var.java:532)
        at clojure.main.main(main.java:37)

EDIT: the solved program now looks like this:

(ns scalc.core)

(defn add [numbers]
  (reduce + numbers))

(defn numchoose []
  (let [nums (re-seq #"\d+" (read-line))]
    (map #(Integer/parseInt %) nums)))

(defn delegate []
  (println "What operation would you like to do?: ")
  (let [operation (read-line)]

    (when (= operation "add")
      (println "You chose to add.")
      (println "What numbers? ")
      (add (numchoose)))))

(defn -main
  [& args]

  (delegate))

Answer 1

For getting the numbers, you can use re-seq:

(re-seq #"\d+" "123 456 789") => ("123" "456" 789")

You still only have strings rather than numbers though. You can use read-string to get the numbers (read-string is convenient, but not safe in all cases. Here we make sure there are really only numbers in these strings so it’s fine).

(read-string "5") => 5

Instead of (apply + numbers) you could use reduce: (reduce + numbers), also your add function really shouldn’t print anything (you should try to separate functional functions from side-effecty functions whenever possible).

This (let [numbers (read-line)] numbers) is equal to (read-line). Don’t overcomplicate things!

Instead of

(if (= operation "add")
      (do ... ))

you can write

(when (= operation "add")
     ...)

when is just a macro that’s useful when you don’t need the else case in your ifs (it wraps everything after the condition in a do, and evaluates to nil when the condition evaluates to false).