ClojureScript

• Type: Defect
• Status: Closed
• Priority: Major
• Resolution: Completed
• Affects Version/s: None
• Fix Version/s: None
• Component/s: None
• Labels:

  None

The cljs.core/apply-to function exhibits incorrect behaviour when called with an "argument count" argc (the second argument to apply-to) greater than or equal to 6.

This is because the cljs.core/gen-apply-to macro produces (essentially) to following function:

(defn apply-to
  [f argc args]
  (let [args (seq args)]
    (if (== argc 0)
      (f)
      (let [[a & args] args]
        (if (== argc 1)
          (f a)
          (...
            (if (== argc 6)
              (let [[f % args] args] ;; f is being overshadowed
                (f a b c d e f)
                (if (== argc 7)
                  (let [[g & args] args]
                    (f a b c d e f g)
                    (...)))))))))))

For (>= argc 6) the f in

(defn apply-to [f argc args] ...)

is being overshadowed by the one in

(let [[f % args] args] ...)

The obvious solution would be to output something like

(defn apply-to
  [func argc args]
  (let [args (seq args)]
    (if (== argc 0)
      (func)
      (let [[a & args] args]
        (if (== argc 1)
          (func a)
          (...
            (if (== argc 6)
              (let [[f % args] args]
                (func a b c d e f)
                (if (== argc 7)
                  (let [[g & args] args]
                    (func a b c d e f g)
                    (...)))))))))))

The following changes to gen-apply-to-helper and gen-apply-to should do the trick:

(defn gen-apply-to-helper
  ([] (gen-apply-to-helper 1))
  ([n]
     (let [prop (symbol (core/str "-cljs$core$IFn$_invoke$arity$" n))
           func (symbol (core/str "cljs$core$IFn$_invoke$arity$" n))]
       (if (core/<= n 20)
         `(let [~(cs (core/dec n)) (-first ~'args)
                ~'args (-rest ~'args)]
            (if (core/== ~'argc ~n)
              (if (. ~'func ~prop)
                (. ~'func (~func ~@(take n cs)))
                (~'func ~@(take n cs)))
              ~(gen-apply-to-helper (core/inc n))))
         `(throw (js/Error. "Only up to 20 arguments supported on ifntions"))))))
         
(defmacro gen-apply-to []
  `(do
     (set! ~'*unchecked-if* true)
     (defn ~'apply-to [~'func ~'argc ~'args]
       (let [~'args (seq ~'args)]
         (if (zero? ~'argc)
           (~'func)
           ~(gen-apply-to-helper))))
     (set! ~'*unchecked-if* false)))

• Assignee:

  Unassigned

  Reporter:

  Kevin Marolt

• Created:

  03/Mar/14 7:22 PM

  Updated:

  05/Mar/14 8:51 AM

  Resolved:

  05/Mar/14 8:51 AM