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I've currently got a function in my main file which squares every number in the list, now that works perfectly with no errors but my unit tests keeps on throwing errors and I cant seem to figure out why.

 (ns squareone.core-test
 (:require [clojure.test :refer :all]
        [squareone.core :refer :all]))

(deftest Squaring
  (testing "Squaring test"
    (is (= [1 16] (square [1 4])))))
  That is everything in my test file

And this is what is in my main file minus the actual squaring function

(ns squareone.core)
(:require '[clojure.string :as string])
(require '['clojure.string :as 'str])

And I get this error

Syntax error (ClassCastException) compiling at 
(C:\Users\public\squareone\src\squareone\core.clj:3:1).
class clojure.lang.PersistentList cannot be cast to class clojure.lang.Symbol 
(clojure.lang.PersistentList and clojure.lang.Symbol are in unnamed module of loader 'app')

Very unsure on how to proceed, any help is appreciated :)

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  • Please check syntax for ns and for require. Parens and quotes. Commented Jan 17, 2021 at 23:24

1 Answer 1

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4

The syntax error is on line 3 which is:

(require '['clojure.string :as 'str])

and we can confirm in a REPL that is indeed illegal:

user=> (require '['clojure.string :as 'str])
Execution error (ClassCastException) at user/eval1 (REPL:1).
class clojure.lang.PersistentList cannot be cast to class clojure.lang.Named (clojure.lang.PersistentList and clojure.lang.Named are in unnamed module of loader 'app')

You also have a problem on line 3, but it doesn't cause a syntax or runtime error:

(:require '[clojure.string :as string])

This attempts to look up the keyword :require in the literal vector [clojure.string :as string] -- the leading quote (') prevents evaluation so that is a symbol (clojure.string) followed by a keyword (:as) followed by another symbol (string). Looking up a keyword :require in a vector is going to return nil.

I expect what you were trying to do was this:

(ns squareone.core
  (:require [clojure.string :as string]))

Note where the parentheses are: the :require form is part of the ns declaration.

At this point, you should be able to delete line 3 and move on to testing.

Why is line 3 illegal though?

The quote (') is shorthand for wrapping a form in (quote ..) and that in turn prevents evaluation. You have three quotes in line 3, so it expands to this:

(require (quote [(quote clojure.string) :as (quote str)]))

The outer quote prevents evaluation, so the argument that is passed to the require function is: [(quote clojure.string) :as (quote str)] which is a vector containing a list with two symbols (quote and clojure.string), a keyword (:as), and another list of two symbols. But require expects just a symbol in those slots like this:

(require '[clojure.string :as str])

and that's the error you are getting: expected clojure.lang.Symbol but got clojure.lang.PersistentList.

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