Clojure Test 4 in coordinate transformation exercise

Exercism
1 
(let [mock-fn (let [n (atom 0)] 
                  (with-meta 
                    (fn [x y] (swap! n inc) [(* x 2) (* y 2)])
                    {:?_current-ns_?/call-count (fn [] (deref n))})) 
        memoized-transform (memoize-transform mock-fn)]
    (= [2 2] (memoized-transform 1 1))
    (= [4 4] (memoized-transform 2 2))
    (= [2 2] (memoized-transform 1 1))
    (= 3 ((:?_current-ns_?/call-count (meta mock-fn)))))

The following is the Test 4 that I am failing.
I understand that a counter is getting inc everytime I call the function with the same arguments.
In clojure there’s a memoize function which makes this example trivial.
My memoize-transform is just using returning (memoize f) which works.
I do not get why the test is asking for call-count to be 3 when clearly the third call should not be run. The correct check should be
((:?current-ns?/call-count (meta mock-fn)))
returning 2, not 3

2

I am stuck here also. Same question as teongleong.

3

Returns a function that memoizes the last result.
I guess it is not to code a generic memorizer, just to remember last call.
So if (f 0 0) and followed with (f 0 0), it will use memorized value.
If (f 1 1) followed with (f 0 0), previous momorized value to be discard.

4

You may be right. If that’s what’s expected, the instruction should make that clear.

Edit: After re-reading the instruction and doc-string, I see that they actually quite clearly asks to check against the last call. I guess we got distracted by Clojure’s built-in memoize function.

5

They also use the word memoization whose standard meaning implies caching every previously-computed result, not just the last one.

The description of this question can be made more precise to remove this ambiguity. I have no idea how/where to report this to someone who can actually make the change, though!

6

Memorization doesn’t imply an unlimited cache. That’s one way to do it. Different implementations may take different approaches to the cache.

You can propose a specific change in this thread and a maintainer may approve and ask for you to open a PR or ask if they should use your proposal to make a PR.