Quil claiming my draw function has 0 arguments

Question

I'm trying to write my first simple graphics app using Quil. Right now, I'm just trying to draw a dot that moves diagonally across the screen.

(ns quil-test.quil-first
 (:require [quil.core :as q])

 (:gen-class))

(defn setup-state []
  (q/frame-rate 60)
  {:x 0})

(defn update-state [s]
  (assoc s :x (q/frame-count)))

(defn draw-state [state]
  (let [x (:x state)]
    (q/stroke-weight 100)
    (q/point x x)))

(q/defsketch quil-first
             :size [500 500]
             :setup setup-state
             :update update-state
             :draw draw-state)

The problem is, running this doesn't show a dot, and the following error is repeatedly printed to the console:

Exception in  :draw  function:  #error {
 :cause Wrong number of args (0) passed to: quil-first/draw-state
 :via
 [{:type clojure.lang.ArityException
   :message Wrong number of args (0) passed to: quil-first/draw-state
   :at [clojure.lang.AFn throwArity AFn.java 429]}]
 :trace
 [[clojure.lang.AFn throwArity AFn.java 429]
  [clojure.lang.AFn invoke AFn.java 28]
  [clojure.lang.Var invoke Var.java 375]
  [quil.middlewares.safe_fns$wrap_fn$fn__114 invoke safe_fns.clj 9]
  [quil.middlewares.bind_output$bind_output$iter__148__152$fn__153$fn__164 invoke bind_output.clj 21]
  [quil.applet$_draw invoke applet.clj 220]
  [quil.Applet draw nil -1]
  [processing.core.PApplet handleDraw PApplet.java 2402]
  [quil.Applet handleDraw nil -1]
  [processing.awt.PSurfaceAWT$12 callDraw PSurfaceAWT.java 1527]
  [processing.core.PSurfaceNone$AnimationThread run PSurfaceNone.java 316]]} 
stacktrace:  clojure.lang.ArityException: Wrong number of args (0) passed to: quil-first/draw-state
 at clojure.lang.AFn.throwArity (AFn.java:429)
    clojure.lang.AFn.invoke (AFn.java:28)
    clojure.lang.Var.invoke (Var.java:375)
    quil.middlewares.safe_fns$wrap_fn$fn__114.invoke (safe_fns.clj:9)
    quil.middlewares.bind_output$bind_output$iter__148__152$fn__153$fn__164.invoke (bind_output.clj:21)
    quil.applet$_draw.invoke (applet.clj:220)
    quil.Applet.draw (:-1)
    processing.core.PApplet.handleDraw (PApplet.java:2402)
    quil.Applet.handleDraw (:-1)
    processing.awt.PSurfaceAWT$12.callDraw (PSurfaceAWT.java:1527)
    processing.core.PSurfaceNone$AnimationThread.run (PSurfaceNone.java:316)

It's saying that my draw-state function takes 0 arguments, when it should take 1. draw-state clearly takes 1 argument though.

I don't understand why draw-state is somehow being "converted" into a 0-arity function.

Answer 1

The problem is I didn't activate "fun(ctional) mode", so the draw function expected to take 0 arguments, since by default state is managed globally.

This works:

(ns quil-test.quil-first
 (:require [helpers.general-helpers :as g]
           [quil.core :as q]
           [quil.middleware :as m])

 (:gen-class))

(defn setup-state []
  (q/frame-rate 60)
  {:x 0})

(defn update-state [s]
  (g/update-with s :x (fn [_] (q/frame-count))))

(defn draw-state [state]
  (let [x (:x state)]
    (q/stroke-weight 100)
    (q/point x x)))

(q/defsketch quil-first
             :size [500 500]
             :setup setup-state
             :update update-state
             :draw draw-state
             :middleware [m/fun-mode]) ; Activate functional mode