Clojurians Log v2
beginners
clojure.set/map-invert is useful when using a hash map as a dictionary and wish to translate in both directions, e.g. encode/decode.
for is often used to generate hiccup for web pages, avoiding a lot of repetitive code.
cycle and rand-nth to generate repeating sequences and random selection, e.g for creating a carousel of video thumbnails on the London Clojurians website.
I've been using a lot of conditional functions recently, and or if when cond
Also using :`clojure-keywords` and {:hash "maps"} as functions to extract data. Hopefully those are fairly well known though š
Hi guys, I built a defprotocol implemented in many defrecord. Here an oversimplified version:
(defprotocol A
(foo [_ b])
(bar [_ b]))
(defrecord R1 []
A
(foo [_ b]
(- b 10))
(bar [_ b]
(+ b 10)))
(defrecord R2 []
A
(foo [_ b]
(* b 10))
(bar [_ b]
(/ b 10)))(= a (-> a (.foo) (.bar))) on all implementations without copying some boilerplate for R1, R2, R3, ... Is there any way to factorize?Right now, I have to copy my tests on all deftest for every defrecord...
Wrap the tests in a function that takes the record as arg?
Hmm, fair enough. Some "utility test functions" including testing sentences.
Also checkout https://clojuredocs.org/clojure.test/are
(are [a] (= a (-> a foo bar))
r1
r2)Actually this is what are is for, my bad for not recommending it at the start
FYI you should not use Java interop to invoke protocol methods on a record, you should invoke the protocol method
Idiomatic question, is this proper clojure idiom to use for updating a data structure based on an expensive calculation?
It's convenient to use let to store a series of intermediate results that depend on previous let values. I'm not sure if that is expected practice.
(defn buncha-calcs
"returns processed-data with a-data and b-data data structure fields updated"
[processed-data input-data]
(let [stage-1 (expensive-calc input-data)
a-results (calc-a (:a-data processed-data) stage-1 )
b-results (calc-a (:b-data processed-data) stage-1 )
]
(assoc
(assoc processed-data :a-data a-results )
:b-data b-results)))
> It's convenient to use let to store a series of intermediate results that depend on previous let values. I'm not sure if that is expected practice.
That's exactly what let is meant for.
assoc can take multiple key-values, which means, you can do this with one call to assoc, like this:
(defn buncha-calcs
"returns processed-data with a-data and b-data data structure fields updated"
[processed input]
(let [stage-1 (expensive-calc input)
a-results (calc-a (:a-data processed) stage-1)
b-results (calc-a (:b-data processed) stage-1)]
(assoc processed :a-data a-results :b-data b-results)))-data suffix from the arg-names. Because Clojure is a very data-centric language, IMO it's reasonable to assume something is data unless mentioned otherwise. This is a personal opinion though.
Now, you are effectively applying the function calc-a to the values of two keys, along with an extra argument. update does this more directly as opposed to manually getting the value, applying the function, and associating it back-in. Looks like this:
(defn buncha-calcs
"returns processed-data with a-data and b-data data structure fields updated"
[processed input]
(let [stage-1 (expensive-calc input)]
(update
(update processed :a-data calc-a stage-1)
:b-data calc-b stage-1)))assoc, dissoc, conj and update are collection-level functions (take a collection as their first arg and return a collection), and compose well with the thread-first macro (`->`), which when used the code becomes more linear to read:
(defn buncha-calcs
"returns processed-data with a-data and b-data data structure fields updated"
[processed input]
(let [stage-1 (expensive-calc input)]
(-> processed
(update :a-data calc-a stage-1)
(update :b-data calc-a stage-1))))
Hi, Iām having this error when publishing to heroku.
Could not transfer artifact net.sf.saxon:saxon:pom:9 from/to jboss (<https://repository.jboss.org/nexus/content/repositories/deprecated/>): Connection reset
This could be due to a typo in :dependencies, file system permissions, or network issues.
If you are behind a proxy, try setting the 'http_proxy' environment variable.
Uberjar aborting because jar failed: Could not resolve dependencies:repositories [["enonic" "<https://repo.enonic.com/public/>"]]
:dependencies [[camel-snake-kebab "0.4.2"]
[clj-http "3.10.1"]
[environ "1.2.0"]
[integrant "0.8.0"]
[integrant/repl "0.3.1"]
[io.xapix/paos "0.2.4"]
[metosin/reitit "0.5.10"]
[org.clojure/clojure "1.10.1"]
[org.postgresql/postgresql "42.2.14"]
[ovotech/ring-jwt "1.3.0"]
[ring "1.8.2"]
[seancorfield/next.jdbc "1.1.613"]
[buddy "2.0.0"]
[clojure.java-time "0.3.2"]
[ring/ring-mock "0.4.0"]
[ring-cors "0.1.13"]]Thanks, that is super helpful