java.io.FileNotFoundException: Could not locate clojure/spec/alpha__init.class or clojure/spec/alpha.clj on classpath

Question

I was trying to understand Clojure spec. While setting up a clojure project I am getting following error while requiring the clojure.spec.alpha:

Exception in thread "main" java.io.FileNotFoundException: Could not locate clojure/spec/alpha__init.class or clojure/spec/alpha.clj on classpath., compiling:
at clojure.lang.Compiler.load(Compiler.java:7391)
at clojure.lang.Compiler.loadFile(Compiler.java:7317)
at clojure.main$load_script.invokeStatic(main.clj:275)
at clojure.main$script_opt.invokeStatic(main.clj:335)
at clojure.main$script_opt.invoke(main.clj:330)
at clojure.main$main.invokeStatic(main.clj:421)
at clojure.main$main.doInvoke(main.clj:384)
at clojure.lang.RestFn.invoke(RestFn.java:408)
at clojure.lang.Var.invoke(Var.java:379)
at clojure.lang.AFn.applyToHelper(AFn.java:154)
at clojure.lang.Var.applyTo(Var.java:700)
at clojure.main.main(main.java:37)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.intellij.rt.execution.application.AppMainV2.main(AppMainV2.java:131)

My project.clj:

(defproject testing "0.1.0-SNAPSHOT"
  :description "FIXME: write description"
  :url "http://example.com/FIXME"
  :license {:name "Eclipse Public License"
            :url "http://www.eclipse.org/legal/epl-v10.html"}
  :dependencies [[org.clojure/clojure "1.9.0"]
                 [org.clojure/spec.alpha "0.1.143"]
                 [org.clojure/core.specs.alpha "0.1.10"]])

and core.clj:

(ns testing.core
  (:require [clojure.spec.alpha :as s]))

(defn foo
  "I don't do a whole lot."
  [x]
  (println x "Hello, World!"))

I will be thankful, if someone can help me out.

Answer 1

I did a lein clean and it started working