What's wrong with this use of rest params with defprotocol and defrecord in Clojure?

Question

What's wrong with the below use of rest params with defprotocol and defrecord in Clojure?

(defprotocol prot
  (f [this] [this & rest]))

(defrecord rec []
  prot
  (f [this] "one arg")
  (f [this & rest] "more than one arg"))

(prn (f (rec.)))
; (prn (f (rec.) 5))
(prn (f (rec.) 5 6))
; (prn (f (rec.) 5 6 7))

The above code prints the output I expect:

"one arg"
"more than one arg"

But if I uncomment either of the commented lines, I get the below exception:

Exception in thread "main" java.lang.IllegalArgumentException: No single method: f of interface: user.prot found for function: f of protocol: prot (bug.clj:10)
    at clojure.lang.Compiler.analyzeSeq(Compiler.java:5376)
    at clojure.lang.Compiler.analyze(Compiler.java:5190)
    at clojure.lang.Compiler.analyze(Compiler.java:5151)
    at clojure.lang.Compiler$InvokeExpr.parse(Compiler.java:3057)
    at clojure.lang.Compiler.analyzeSeq(Compiler.java:5371)
    at clojure.lang.Compiler.analyze(Compiler.java:5190)
    at clojure.lang.Compiler.analyze(Compiler.java:5151)
    at clojure.lang.Compiler$BodyExpr$Parser.parse(Compiler.java:4670)
    at clojure.lang.Compiler$FnMethod.parse(Compiler.java:4328)
    at clojure.lang.Compiler$FnExpr.parse(Compiler.java:3173)
    at clojure.lang.Compiler.analyzeSeq(Compiler.java:5367)
    at clojure.lang.Compiler.analyze(Compiler.java:5190)
    at clojure.lang.Compiler.eval(Compiler.java:5421)
    at clojure.lang.Compiler.load(Compiler.java:5857)
    at clojure.lang.RT.loadResourceScript(RT.java:340)
    at clojure.lang.RT.loadResourceScript(RT.java:327)
    at clojure.lang.RT.loadResourceScript(RT.java:319)
    at clojure.main$load_script.invoke(main.clj:220)
    at clojure.main$script_opt.invoke(main.clj:273)
    at clojure.main$main.doInvoke(main.clj:354)
    at clojure.lang.RestFn.invoke(RestFn.java:409)
    at clojure.lang.Var.invoke(Var.java:365)
    at clojure.lang.AFn.applyToHelper(AFn.java:163)
    at clojure.lang.Var.applyTo(Var.java:482)
    at clojure.main.main(main.java:37)
Caused by: java.lang.IllegalArgumentException: No single method: f of interface: user.prot found for function: f of protocol: prot
    at clojure.lang.Compiler$InvokeExpr.<init>(Compiler.java:2880)
    at clojure.lang.Compiler$InvokeExpr.parse(Compiler.java:3063)
    at clojure.lang.Compiler.analyzeSeq(Compiler.java:5371)
    ... 24 more

Why is this?

Answer 1

As far as I can tell, protocols do not support variadic arguments. What's probably happening is that "&" is taken as an argument symbol instead of a variadic indicator / list comprehension.