Clojurians Log v2

So I think I am feeling some of the pains of printing with lazy stuff. What’s the ‘proper’ way to do this? I basically map over a list of commands and run sh on it (this is a babashka script) but I get the prints of everything before the actual invocation of the command

Is it just do to a doall? I call my shell func repeatedly and that seems to be the main culprit

Reduce or run! Could be helpful, depending on what you need from the result of the calls

yeah I need just a list of the results, so dorun won’t work, and I could get reduce to work but doall does exactly what I need

I am basically timing how long something takes and want to run it a few times to get an average

@grazfather https://stuartsierra.com/2015/08/25/clojure-donts-lazy-effects

Are there any good video tutorials on using Clojure from the ground up? Not just “this is the language” but rather “this is how you set up a good dev environment and how you design and deploy a Clojure application”. It’s totally fine if it’s focused on the language as well as the other parts are there as well. Paid courses are OK.

https://www.jacekschae.com

I think that is the best in this topic

How about this too? https://practicalli.github.io/clojure/ and his set of very good videos? https://www.youtube.com/channel/UCLsiVY-kWVH1EqgEtZiREJw

Hello, I have a very weird situation in my REPL (`lein repl`) that can not be normal behavior https://pastebin.com/QC3RtQgj How can require be not available from everywhere :thinking_face: O I am doing something stupid? :face_with_hand_over_mouth:

Perhaps this explains that behaviour: https://clojuredocs.org/clojure.core/in-ns#example-542692cdc026201cdc326d13

i'm not an expert, but

(ns newgsheet3.core
     (:require [clj-time.core :as time]
             [google-apps-clj.credentials :as gauth]
             [google-apps-clj.google-drive :as gdrive]
             [google-apps-clj.google-drive.mime-types :as mime-types]
             [google-apps-clj.google-sheets-v4 :refer :all :as gsheets])
     (:import [com.google.api.services.sheets.v4.model CellData RowData]))

(require '[<http://clojure.java.io|clojure.java.io> :as io])

what to require to have source and doc available in my REPL it is available in 'user namespace?

(apply require clojure.main/repl-requires)

that's exactly how a clojure main repl starts up.

Yeah, in-ns catches a lot of people out. When you use it on a "new" namespace that has not been loaded (via require), you get a completely "empty" namespace: with not even clojure.core referred into it.

A good rule of thumb is "never use in-ns" (but of course there are times when it is useful).

Another good rule of thumb is "never type into your REPL" (always evaluate code from your editor), which also side-steps this issue.

Evening all. I'm just starting and the overall Clojure syntax is giving me a bit of a headache. Could some one shine some light to why these two are not equal? (for [x [1 2 3]         y [1 2 3 4]         :when (not= x y)]     [x y])  (def a [1 2 3])  (def b [1 2 3 4])  (for [a b :when (not= a b)][a b])

They evaluate as follows: ([1 2] [1 3] [1 4] [2 1] [2 3] [2 4] [3 1] [3 2] [3 4]) ([1 [1 2 3 4]] [2 [1 2 3 4]] [3 [1 2 3 4]] [4 [1 2 3 4]])

I was experimenting in http://nextjournal.com . I wonder can I see some sources of functions but (apply require clojure.main/repl-requires) because I guess it is CLJS. Also this environment is more like REPL as far as I understand.

You likely meant a a b b in the second for

I may have misunderstood how the a and b expand inside the for statement

Imagine it is a let

The difference is in a let a name is bound to the given value, but in a for a name is bound to each element in the given seq

I'll need to spend some time with this, it seems 😄

Thank you for the help.

I personally find for quite difficult, I was told you should mostly use Map or Filter

Seems I need to read it as "For a in a and b in b ..."

for can definitely be counter-intuitive/surprising for folks coming to Clojure from other languages where for is a loop rather than a comprehension.

Once you get used to it, it can sometimes make code a lot more readable than a combination of map and filter -- if you specifically need some lazy processing of data.

@email113 Specifically for your example, you can get there in a series of small steps that transform your code:

(for [x [1 2 3] y [1 2 3 4] :when (not= x y)] [x y])
;; define a and b as you have above
(for [x a y b :when (not= x y)] [x y]) ; pure substitution of value with symbol bound to same value
(for [a a y b :when (not= a y)] [a y]) ; rename local symbol x to a
(for [a a b b :when (not= a b)] [a b]) ; rename local symbol y to b

So I could use any unused variable name inside the for that I just need to assign/bind(?) to a and b respectively, something like: (def a [1 2 3]) (def b [1 2 3 4]) (for [asdf a hjkl b :when (not= asdf hjkl)] [asdf hjkl]

I think the re-use of the variable name threw me a bit

@email113 the names bind to the elements of sequence a and b respectively. Not to the sequences themselves.

Right, hence hiredman's comment that it is like let: for introduces new, local symbols bound to (elements of) sequences, as does loop (which also isn't like loops in other languages).

Noob here Is there a way to use some-> with & args? For instance: (defn f [x & funcList] (some-> x funcList)) ?

there's probably a cleaner way to write it, but it can be accomplished with reduce:

(reduce (fn [x f]
          (let [new-x (f x)]
            (if new-x
              new-x
              (reduced nil))))
        1
        [inc
         inc
         ;; (constantly nil)
         inc])

Is there a way to write a macro to do this?

There's not much benefit in writing a macro for this example. You could write a function that does this.

It possibly already exists in clojure.core.

@smith.adriane If x is nil, you would want to short-circuit that earlier, which simplifies the code anyway: (reduce (fn [x f] (if (some? x) (f x) (reduced nil))) x func-list)

What does it do?

I want to pass in some parameter x followed by a list of functions fList

A single call to the outer function should feed x into the first function in fList, pass that result into the 2nd, etc. until all functions have been called

I wrote a function that does this, but I'm trying to learn Clojure libraries so I wanted to check if there's a well known function that already does that

But you also want to stop when you hit a nil right?

Otherwise you could just do ((apply comp func-list) x) or (reduce (fn [x f] (f x)) x func-list)

yeah I was thinking comp 😄

https://clojuredocs.org/clojure.core/comp

relevant things: apply juxt comp partial

So I have a question. Sometimes users have an outdated copy of the login page for one of our applications. Which throws an anti-forgery error when they try to log in. Is there a way to make sure the page is fetched freshly when they open it up even if its cached? Or is there some straightforward solution to this outdated x-csrf token?

maybe javascript?

Seems like

<meta http-equiv="Cache-Control" content="no-cache, no-store, must-revalidate" />

from https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control : > no-cache > The response may be stored by any cache, even if the response is normally non-cacheable. However, the stored response MUST always go through validation with the origin server first before using it, therefore, you cannot use no-cache in-conjunction with immutable. If you mean to not store the response in any cache, use no-store instead. This directive is not effective in preventing caches from storing your response. > > no-store > The response may not be stored in any cache. Note that this will not prevent a valid pre-existing cached response being returned. Clients can set `max-age=0` to also clear existing cache responses, as this forces the cache to revalidate with the server (no other directives have an effect when used with `no-store`).

I think the no-cache is superfluous alongside no-store