Clojurians Log v2

transients don't replace hash-maps, they are an optimization for code that builds up hashmaps, so they lack many of the read-oriented features

You don't need to do anything, #(nth % 1) is a function of one argument

(->> [1 2 3]
  (#(nth % 1)))

But in the more general case, you can nest ->> inside -> or use as->

(-> [1 [2 4 6] 3]
  (nth 1)
  (conj 10)
  (->> (map inc)))

As well as do what you did, and wrap it in an anonymous fn (you just need to call the fn as well).

Finally, if you really want a flip, its pretty trivial to implement yourself:

(defn flip [f & args]
  (apply f (reverse args)))

Despite having updated to the latest CIDER nrepl 0.25, my repl was only using 0.22. After some more research, I seem to have solved my problem by updating my ~/.lein/profiles.clj. I removed references to CIDER as https://jakemccrary.com/blog/2017/08/27/my-current-leiningen-profiles-dot-clj/ stated that the latest CIDER no longer requires you to list dependencies explicitly. Feels like a big DUH after fixing this. Thanks for pointing me in the right direction @dpsutton 🙏

My last little foray into clojure went really well. I have another idea I could use some validation for, as well as some direction on how to approach it. I watched a Pharo Smalltalk demo and thought the codebase visualization and reflection metrics were really cool. What I'd like to do is be able to parse a clojure codebase, run some metrics on that codebase, and then generate some visualization tools and maybe even a way to traverse the codebase. Some simple ideas might be showing the number/location of references to a function. Showing a hierarchy of macro usage, along with some example inputs/outputs that show macro expansion. In general being able to generate a graph of the codebase that spans out from the entry point(s). Would this type of tool be at all useful? Is there something like this already out there? If it would be useful, what are some additional things that also might be nice to have with a tool like this? Lastly, if I were to attempt this, what would be a good way to approach it? I'd really like to be able to fully parse the contents of a file/codebase so that I can have all the semantic information I need without having to resort to hacks/tricks.

Can anyone explain why I would use force with a delay? We already have @ and deref and it seems to me they do exactly the same thing

Why do I get here a error :

(defn to-json[suspects]
  into {} (clojure.string/join( ", " (get :name suspects) (get :glitter-index suspects))))


(to-json {:name "Roelof" :glitter-index 2})

; Execution error (ClassCastException) at chapter4/to-json (form-init1060733672431633963.clj:82).
; class java.lang.String cannot be cast to class clojure.lang.IFn (java.lang.String is in module java.base of loader 'bootstrap'; clojure.lang.IFn is in unnamed module of loader 'app')

because you wrote clojure.string/join(", " ...)

to call a function in clojure you must use sexp form like this (clojure.string/join ", " ...)

thanks

still no luck

(defn to-json [suspects]
  (  into {} (clojure.string/join ", " [(get :name suspects)])))


(to-json {:name "Roelof" :glitter-index 2})

; Execution error (IllegalArgumentException) at chapter4/to-json (form-init1060733672431633963.clj:82).
; Don't know how to create ISeq from: java.lang.Character

get takes the map first and then the key

(get suspects :name)

join will return a string calling (into {} “some string”) will throw that exception

maybe you can describe what you trying to achieve?

also [(get :name suspects)] is a vector with one entry, so string/join won't have anything to join

I kniw

what I try to achieve is to convert this : {:name "John", :glitterindex: 2) into a json without using a json library

so the outcome is {"John Doe", 2}

(def foo {:name "John Doe" :glitterindex 2})

(apply hash-map (vals foo))

{"John Doe" 2}

maps in clojure is unordered so vals might return [2 "john"]

However, here be dragons, json processing is very edge casey, lots of work arounds and cavets - hence a trivial translation won't suit

I would just use a library tbh and @delaguardo is right 🙂

thanks, but I still think the purpose of the challenge of the brave book was to do it manually

Then you can use juxt to extract values under certain keys from a map

juxt ?? That one is not explained in thir or a former chapter

could you share a link to your current chapter?

otherwise I can only guess what you are trying to do)

sure: https://www.braveclojure.com/core-functions-in-depth/

ok, so is it exercise 4 you are working on?

Ah I just did that one

if that's ok with you I can share my solution

but I was converting to CSV

yep, the lastest ine

@antbbn of course you may. Maybe I find some ideas I can use

force is agnostic about whether its argument is actually a delay

user=> (force 42)
42

and @ is already just a reader shorthand for deref

(defn get-many
  [ks record]
  (map #(get record %) ks))
(defn suspects-to-csv 
  [suspects]
  (let [header-keys (keys (first suspects))]
    (reduce #(clojure.string/join "\n" [%1 %2]) 
            (clojure.string/join "," header-keys)
            (map 
             (comp (partial clojure.string/join ",") (partial get-many header-keys))
             suspects))))

I used a let block to make sure that I always extract the keys in the same order

using get-many

get-many could just be (map record ks) if you are using normal hash maps

also, keys and vals will always return the same order for two collections with the same keys

finally your string/join calls could be str calls, if performance is a concern at all you could use a StringBuilder instead

mhh I lost part of the conversation

yeah, slack is being weird

but now that I think about it totally makes sense that keys and vals will keep the order for the same collection

(the main reason to use join instead of iterating str calls is performance, using small calls to join in a loop like this undoes that advantage)

I guess the one gotcha is an ArrayMap vs. HashMap, which I didn't consider at first

Hi, I have a map and i want to fetch the keys which has more that 10 value, How can I get it

{"hello" 10, "hi" 12}

output should be {hi 12}

Use filter

(sorry, hi first !!)

ok thanks - I can't really think of a use case for that but I guess it was important to someone :)

@popeyepwr (into {} (filter #(< 10 (val %)) coll)) (if the hint to "use filter" isn't enough on its own)

Maps in clojure are not ordered. For ordered maps see https://github.com/flatland/ordered

PersistentArrayMap is, PersistentHashMap isn't, and past 8 pairs the former is "upgraded" to the latter

so you think it's a good idea to make sure that you get the keys in the explicit order you want using something like (map record ks)

if you want order, use ordered linked above

Although the order of keys (or vals) is "random", they are consistent: whatever order keys gives you matches whatever order vals gives you.

gotcha, it's only that the gist of that exercise was to convert that list of hash maps to a csv

and given that each map is a different element of the list even though they have the same keys

I was worried about the case where vals of one item might return them in a different order than vals of another item

Right, I think your overall approach -- get keys from the first hash map and use that, in order, to get values from the other maps makes sense. You can't rely on vals producing the same order of keys across multiple hash maps.

sorted-map or sorted-map-by can also be used to ensure a definite order on keys

another thing that I noticed looking at my code is that I reduce over the result of a mapping over the list of suspects

but It could also be refactored to reduce over the suspect by using a slightly more complex function

like so

(defn suspects-to-csv 
  [suspects]
  (let [header-keys (keys (first suspects))]
    (reduce (fn [result m]
              (str result 
                   "\n" 
                   (clojure.string/join "," (map m header-keys))))
            (clojure.string/join "," header-keys)
            suspects)))

which style would be more idiomatic?

Nice! thanks for the tips

I’m fiddling to setup test files and CLI commands to run it using deps.edn. If anyone could point me out to any reference that would be helpful.

https://clojure.org/guides/deps_and_cli https://clojure.org/reference/deps_and_cli

@claudius.nicolae maps are not ordered, but to PersistentHashMap instances with the same keys will have a keys output and a vals output in the same order

PersistentArrayMap is ordered, PersistentHashMap isn't

Is there any sample projects that I can look upto? I referred to @seancorfield’s https://github.com/seancorfield/dot-clojure/blob/develop/deps.edn. And added below,

:test   {:extra-paths ["src/test/clojure"]
          :extra-deps  {org.clojure/test.check {:mvn/version "RELEASE"}}}

 :runner {:extra-deps {com.cognitect/test-runner
                       {:git/url "<https://github.com/cognitect-labs/test-runner>"
                        :sha     "b6b3193fcc42659d7e46ecd1884a228993441182"}}
          :main-opts  ["-m" "cognitect.test-runner"
                       "-d" "test"
                       "-d" "src/test/clojure"]}

I didn't say it was orderd, I said vals or keys on two PersistentHashMap with the same keyset have the same order

@kannangce Check clojure -Sdescribe -- I suspect you're on an old version.

Most of my projects assume 1.10.1.727 or higher.

(ins)user=> (def m1 (into {} [[:a 0] [:b 1] [:c 2] [:d 3]]))
#'user/m1
(ins)user=> (def m2 (into {} [[:a "a"] [:b "b"] [:c "c"] [:d "d"]]))
#'user/m2
(ins)user=> (= (keys m1) (keys m2))
true

For example https://github.com/seancorfield/clj-new and https://github.com/seancorfield/depstar both state 1.10.1.727 or higher as a requirement in their READMEs (my dot-clojure does not, but it probably should).

Yes, Sean said that too.

Hi, my question is probably very dumb and apologies for that. I’m trying to understand how this compojure-api code works (app (-> (mock/request :get "/api/documents?id=123")) works behind the scene. I printed in the repl both app and the mock request , you can find them here. https://paste.ofcode.org/gYrXDmzUzHTiYrQvKSzsxD what I don’t understand is how (app mock-request) is executed. I can’t find the function that receives the request. Also is not clear to me what #Route is printed just before any dictionary. Thanks for any help in advance.

All of my projects use deps.edn for testing these days -- https://github.com/seancorfield/next-jdbc/ is a good example since it has both GitHub Actions and CircleCI configured to run tests via deps.edn

My version is “1.10.1.727”. But not sure why running clj -M:test or `clj -M:runner` takes me to repl. Will check some of your projects and compare my deps.edn. Thanks Sean!

@francesco.losciale #Route{} is a print format for a record called Route

Aren't the :test and :runner aliases meant to be run together? like so: clj -M:test:runner Not sure about :runner on its own but the :test alias doesn't have a :main-opts entry, so I think it makes sense that it takes @kannangce to a repl, no? :thinking_face:

defrecord creates a type that acts like a hash map, but has its name prefixed when printing, and allows custom extension of protocol methods

See https://skillsmatter.com/skillscasts/3445-functional-web. Note: Compojure is old and slow O(n); works well with few routes, but generally prefer https://github.com/metosin/reitit.

Oh, well spotted! Yes, you need -M:test:runner

But clj -M:runner should not give you a REPL -- I would expect in most projects for it to give you an exception since you won't have any test dependencies added in.

For example:

(! 511)-> clojure -X:new :name kannan/example
Downloading: seancorfield/clj-new/maven-metadata.xml from clojars
Generating a project called example based on the 'lib' template.
The lib template is intended for library projects, not applications.
(! 512)-> cd example/
(! 513)-> clojure -M:runner

Running tests in #{"test"}
Execution error (FileNotFoundException) at cognitect.test-runner/test (test_runner.clj:62).
Could not locate kannan/example_test__init.class, kannan/example_test.clj or kannan/example_test.cljc on classpath. Please check that namespaces with dashes use underscores in the Clojure file name.

Full report at:
/var/folders/p1/30gnjddx6p193frh670pl8nh0000gn/T/clojure-3814224161163105319.edn

@antbbn thanks for showing me this

For what it's worth, here's what I'm getting in each case (this is for a project that doesn't have any tests yet):

> clj -M:test       
Clojure 1.10.1
user=> 

> clj -M:runner

Running tests in #{"test" "src/test/clojure"}

Testing user

Ran 0 tests containing 0 assertions.
0 failures, 0 errors.

> clj -M:test:runner

Running tests in #{"test" "src/test/clojure"}

Testing user

Ran 0 tests containing 0 assertions.
0 failures, 0 errors.

Hey I did a full answer then, but making o e answer in multiple message was not a good idea with slack outage. The full answer never arrive !!

@noisesmith Not quite. keys and vals are only guaranteed to return orders consistent with each other for the same identical map object. While it is common for two PersistentHashMap objects that are = to return the same order as each other for keys (or vals), that is not guaranteed, and can be false when two keys have the same hash value, but were added to the not-identical-but-= PersistentHashMap instances.

Example:

$ clj
Clojure 1.10.1
(clojure-version)
"1.10.1"
(hash 0)
0
(hash 92612215)
0
(def m1 (-> {} (assoc 0 :added-first) (assoc 92612215 :added-second)))
#'user/m1
(def m2 (-> {} (assoc 92612215 :added-first) (assoc 0 :added-second)))
#'user/m2
m1
{0 :added-first, 92612215 :added-second}
m2
{92612215 :added-first, 0 :added-second}
(= m1 m2)
false
(keys m1)
(0 92612215)
(keys m2)
(92612215 0)

This happens because PersistentHashMap puts all keys with the same hash value into the same "hash bucket", which is simply a linked list of elements, in the order that they were last added to the PersistentHashMap

thanks for the info

Reducing without building intermediate sequence first can be faster -- I'd think only noticeably so with larger sequences. As a beginner I usually find separate reduce and map steps sometimes easier to manipulate in code, but that's probably highly editor/user-dependent. I'd be surprised though if one of the two variants was less idiomatic than the other -- I'd expect readability/style preference to be criterium of choice here.

Makes sense, also I agree that in this context and as a beginner reducing over something that is already mapped seems more straightforward

@pavlos Yup, it's going to depend on exactly what's in your project, with -M:test producing a REPL (since there's no :main-opts in that alias) and -M:runner either failing (as I showed above in a freshly created project) or finding no tests to run as you saw.

hi all, im using cljs with reagent which produces an html and a js. My backend webserver is trying to render the page with jinja2 and i wanted to load the page with some data (it's a json object or an array in practice). How can i 'access' this data in cljs?

you can use inline js to embed the data in the page, and then access the data with cljs interop

more commonly the rendering happens in cljs and the data is fetched via AJAX from the server

I guess i could do ajax here but im changing the design from being written in straight js to cljs and thats how it currently works. I'll look into ajax though, thanks