Compojure/Ring Routing Error: Wrong # of Arguments

Question

The route setup detailed below causes the error: Wrong number of args (0) passed to: PersistentArrayMap Can anyone help me understand this error and how to resolve it?

(defn sign-in [req]
  ({:status 200 :body "hello world" :headers {"content-type" "text/plain"}})) 

(defroutes paths
  (GET "/connect" {} connect-socket)
  (POST "/sign-in" {} sign-in)
  (route/resources "/")
  (route/not-found "Resource not found."))

(def app
  (-> (defaults/wrap-defaults #'paths defaults/api-defaults)
      wrap-json-params))

Answer 1

fix your sign-in function by unwrapping the response map

(defn sign-in [req]
  {:status 200 :body "hello world" :headers {"content-type" "text/plain"}}) 

the problem is, you put a map in a function position (first element of a list) and it requires a argument.

(
  {:status 200 :body "hello world" :headers {"content-type" "text/plain"}} ;; function
  ???      ;; argument
 )

in clojure, map can act as a function with key as its argument and returns value of that key, ex

({:a 1 :b 2 :c 3} :a)
=> 1