Hi, Joker says my do blocks are redundant, what does it mean?

Hi, Joker says my do blocks are redundant.
What does it mean?
(defn request-rows
  [range robot]
  (loop [i range]
    (when (> i 0)
      (do (tags/request-tag (str "ROBOT_" (:id robot) "_ROW_" i "_FISH_CELL_ID") 6000))
      (for [feeder (:feeders robot)]
        (do (tags/request-tag ((str "ROBOT_" (:id robot) "_ROW" i "_AMOUNT_LEFT_TO_FEED_"(:id feeder))) 6000)))
      (recur (dec i)))))

@ozfraier many clojure macros (including loop, fn, and when,) contain an implciit do

@ozfraier also do with only a single form in it is always redundant

(do x) can be replaced with x, in any case where (do x) is valid

Thank you, I will try to do without the do

Wu wei

on that note, try is usually not needed either :D

Question about clojure's == equality test. so I get that it is equality check with an additional type check, but when I do:

(== 1 1.0) ;;true
(== "X" \X) ;; false

check (doc ==)

and i'm not trying to be snippy. i honestly didn't know the answer but trying to show you how i knew where to look to find an answer

there's nothing in clojure or java that considers "X" and \X the same

you could make your own test function of course #(= (str %1) (str %2)) or more generally #(apply = (map str %&))

@sunchaesk I don't get false, I get an exception from that second comparison:

user=> (== "X" \X)
Execution error (ClassCastException) at user/eval143 (REPL:1).
class java.lang.String cannot be cast to class java.lang.Number (java.lang.String and java.lang.Number are in module java.base of loader 'bootstrap')
user=>

As @dpsutton says, if you look at (doc ==) it says that it works with "nums" so I'm not sure how/where you're running that == between a string and a character?

likely cljs not clj

then even easier i suppose > Returns non-nil if nums all have the equivalent > value, otherwise false. Behavior on non nums is > undefined.

Yeah, same thing, just explains the lack of an exception

Ah, yeah, cljs having different behavior to clj makes sense(!).

Hello 👋, first time poster. Working my way through Clojure for the Brave and True and confused on the example below. Why does the vector need the extra braces?

(into {:favorite-emotion "gloomy"} [[:sunlight-reaction "Glitter!"]])
; => {:favorite-emotion "gloomy" :sunlight-reaction "Glitter!"}

(into existing-map [ [key-1 val-1] [key-2 val-2] ]

putting space around them to make them not bleed together. its a vector. each element of which is a two element vector, key and value

so the vector doesn't need extra braces, its a vector of two element vectors

Thanks for the quick reply! Clears it up perfectly.

the way maps work, the input could have been [{:sunlight-reaction "Glitter!}] as well - you don't see this form as often though

Interesting, I feel like I see that all the time in JavaScript. An array of objects.

right, a map accepts either a map, or a vector (treated as a key-value pair, must be exactly length 2)

there's also assoc which takes a freeform series of keys and values

That's the difference and which is pretty mind bending for a humble JS dev learning Clojure.

user=> (assoc {:a 1} :b 2 :c 3)
{:a 1, :b 2, :c 3}

we use maps a lot, so we have many features and conveniences around them

Oh, I didn't know about assoc yet, wow.

@ozfraier even if when and for didn't have implicit do , your code still doesn't make much sense to me. Why are you wrapping single expressions in explicit do 's? do is only useful for grouping multiple expressions.

@jason358 I refactored a do block that had multiple expressions into a for block, Also, I felt like I needed the do to run the request-tags function immediately for side effects, but that may be voodoo programming.

"immediately" as in "not lazily"? do doesn't do anything for non-laziness, iirc

Clojure is not a lazy-by-default language anyway, it doesn't make sense

if your expr is in "lazy" context, wrapping it in do still does nothing, your do will now be in the same "lazy" context

cf.

user=> (do (for [a [1 2 3 4]] (println a)) 1)
1
user=> (do (for [a [1 2 3 4]] (do (println a))) 1)
1

I think I confused do an doall in that case. What about

(doall (for [a [1 2 3]] (println a)))

I wonder if there is a clojure repl for the smartphone :P

There is one called replete for anyone interested :)

doall does the trick, but what you are really looking for is doseq 🙂 as in (doseq [a [1 2 3]] (println a))

cool, thank you for explaining

If I have code like this,

{:x (f)
 :y (g)}

I dont think so, cause at map order is random.

yeah, before (f) runs, it is read (to create the symbol inside a list, which eval then compiles and runs), and the reader is what creates the hash map and is allowed to change the order

@hindol.adhya on the other hand: (hash-table :x (f) :y (g)) will always call f before g, since the map is created after eval

@hindol.adhya I would not rely on that. I would go for (let [x (f) y (g)] {:x x :y y})

Okay, then I will use let as well.

@teodorlu it's fine to dislike it on style grounds, but it's an explicit promise that args are evaluated left to right

@noisesmith I was referring to @hindol.adhya’s example

Sidenote: if you rely on the order of f and g, they probably have some side effect. I'd consider renaming to f! and g!.

@teodorlu I have considered that. They both read from a reader. I ended up not adding ! mostly due to preference.

Yeah, in that case I might agree. Hard to come up with a general rule. Clojure internally isn't 100 % strict on this either, both slurp and spit are missing !

and read and println and ...

mhm

Hello everyone, I wanted to use `comment` macro  as java `/ /` analog

(comment
  1todo
  )

1. Caused by java.lang.NumberFormatException
Invalid number: 1todo

I don’t think there is. The reader has to read the complete (comment ... ) form, and it can’t do that if there’s an error inside the form.

Okay, got it , thank you!

If I have a collection of a collection of strings, let's say

[["hello" "world"]["hello" "mars"]["hello" "moon"]]

'("hello world" "hello mars" "hello moon") ;;I don't really mind the type of collection

(map #(clojure.string/join " " %) [["hello" "world"]["hello" "mars"]["hello" "moon"]])

Cool 🙂 actually, the space was not really part of the problem 😅 I came up with (map #(apply str %) [["a" "b" "c"]["d" "e" "f"]])

yep, that'll work too if you don't need the space

@e2d4f6 I use #_ instead of comment, it's more powerful

user=> #_(1todo)
user=>

it doesn't even care about classic issues like unbalanced hash-maps:

user=> #_{1todo}
user=>

user=> #_{1todo} 42
42

hi, I don't know what is wrong with this:

(comment
  (defn destructure [aa] (println aa)
    ;(let [{:keys [c d]} :as aa]
    ;  (println c " " d " ")
    ;  )
    )
  (let [xx {:a 3 :b 4}] (destructure xx))
  )

I get Unsupported binding form: :a

it's realy frustrating since I am reading the docs and I can't figure out whare I'm going wrong

In your let, you don’t want the :as there.

yeah, the :as belongs inside the hash-map, but aa is already bound, so you don't want it at all

well, the code as it is does not work

please ignore the ; comments

(let [xx {:a 3 :b 4}] (destructure xx)) i think is the only code under discussion?

yes

the answer is do not call destructure at all

pretend that doesn't exist

another issue is clojure.core/destructure exists and wouldn't like your map most likely

but not clear what you are trying to achieve

aaa

I think the code as pasted is fine?

I'm trying to learn how to destructure function parameteres

it would be, if that destructure was the one he was calling when he called destructure :D

yeah exactly 😄

my goal is to have (defn [a b {:keys [x y]}) (println ))

the error message in repl could be more helpful

you can use *e to see the full previous error, including stack trace etc.

that's often enlightening

oh i'm sorry. i didn't put together your destructure . my mind went to clojure.core/destructure. that's why i said pretend that doesn't exist. i'm sorry for my confusion

eg. the stack trace would have revealed that clojure.core/destructure was called, and not the one in your ns, most likely

ok, so thanks to your help I figured it out - I was loading the whole file in repl - but my function was inside (comment ) so it was not created

that is why it failed and was harder to get to the cause

thanks for your time

that seemed surprising to me :)

haha I saw you almost replying before, I am glad I got the chance to correct the misinfo

#_ works by reading then discarding so seemed like it still has to read just as much as comment

Hey everyone. Could I please get some guidance on how to organize projects and deploy them to a cloud platform? For a simple scenario, I would like to have a client (re-frame) and server (some REST Api framework) projects. AWS Beanstalk SE platform seems to assume these would be bundled/deployed as one application which isn’t ideal - it would be nice to treat these as components that can be updated separately. Beanstalk Docker adds additional overhead. Any help would be very appreciated. I’m open to other cloud platforms. Thank you!

I'm using clj -m namespace-name to call the -main function from the command line. It seems to not just run -main, but all functions in the namespace? Is there a way to run just -main?

hello all! I am working with clojure spec. Does anyone know the best way to express s/def for a value that must either be a non blank string or nil? For then non-blank part I have (s/and string? (complement str/blank?))

you could wrap that in (s/nilable ...)

yes.. thought about that but that but then I must wrap both predicates?

(nillable (complement str/blank?))

and (nilable string?)

I would do (s/nilable (s/and string? (complement str/blank?))) I think

nilable is optimized to cover the nil case so it's better at the top level

ah ok

Thanks. I'll try that out 🙂

I've come to believe it would probably be useful to have a pred/spec specifically for non-blank strings

given that it's both common and cumbersome

Well there you have my little contribution to clojure spec 😉

hehe

well it wouldn't be that - we can optimize the impl

and the generator

ok

I think the example above should gen

Yes. Worked fine 🙂

thanks!

love your talks by the way 🙂

thx!

(def d {:one {:two {:three 3 :four 4 :five 5}}})

How to get :three and :five from that?

Use get-in

So 2 get-in?

Ya, one call to get-in for each

You can also use destructuring if you prefer

Something like (-> d (get-in [:one :two]) (select-keys [:three :five])) should work as well.

With destructuring: `(let [{{{:keys [three five]} :two} :one} d] [three five])`

But my personal favourite is just two get-in with a let, or a let where you get the inner map and then use that to extract three and five using keywords. Simple and readable

I also prefer to use -> over get-in

Reasonable points for sure.

`(let [two (-> d :one :two) three (:three two) five (:five two)] [three five])`

Where did inner come from?

Is that arbitrary?

Oups

Edited

there's also (-> d (get-in [:one :two]) ((juxt :three :five))) though most people hate to see (( inside ->

Clojure, where "there's always many and --preferably even more-- non obvious ways to do it"

Although all ways will be obvious to you once you're told about them hehe

Ok thanks for that juxt is going to solve some other stuff for me too, what a useful but non-obvious function, no idea it was there

I find it pleasing, writing a function that has juxt in it is almost like writing a haiku

people get enamored with juxt

which is reason to be suspicious of it, of course :D

has a tendency to be overused when you first discover it 😉

It's way more fun to use a juxt, but much more pleasant to read code using a let

I'm reminded of that old copypaste which I can't seem to find now, where the beginner haskell programmer uses '1 + 1', the grad student uses a Peano arithmetic implementation, the phd does the Peano calculation in the type checker, and the expert uses '1 + 1'

meanwhile, juxt is like the first 'functional programming thingy' I ever remember learning, and I just remember thinking 'ok, so this this is it, juxt, map, reduce, monads...', I even implemented it in PHP for some ghetto web 'framework'. And then never used it again

Is it possible to use lein checkouts without having to restart the repl everytime?

once the checkout is set up, you should be able to reload the library files as you edit them

using the :reload or :reload-all arg to require, or whatever shortcut your editor offers

even without a checkout load-file will redefine the ns from a file, and the checkout makes sure you see the changes if you restart too

I must not be doing something right because the changes are not taking effect

sometimes what I do is insert a deliberate error (like a garbage token at the top of the file) to prove whether the file is loaded from what I'm editing or not

I have some printlns that I am doing to see if the changes took effect but the outputs is still the same

but there are things that would prevent the printlns if they are not at the top level (eg passing a function isntead of var to a long lived process, attempting to redefine a defmulti...)

@mario.cordova.862 what does (io/resource "m_ns/my_file.clj") return - it will show the actual path that clojure uses when reloading

(that is, the path to your ns, without the containing directories)

eg.

scratch=> ( "clojure/core.clj")
#object[.URL 0x25d61f8d "jar:file:/Users/justin.smith/.m2/repository/org/clojure/clojure/1.10.1/cloju
re-1.10.1.jar!/clojure/core.clj"]

which shows I get clojure via a jar in m2

with a checkout that's set up properly, it should return the path to the file on disk in the original project

The dependency file I want reload is called corefuncs.clj and its namespace is myns.corefuncs and when I call ( "myns/corefuncs.clj") I get #object[.URL 0x3e4eea1 "jar:file:/path/.m2/reporistory/path/myns/corefuncs.clj]

And then it returns the actual file contents

so your checkout isn't set up

Hmm its because its looking into the .m2 folder?

it actually has jar!/... in the middle there

Yes

I know that because the URI is a jar URI

you can't hot reload from the jar, because you didn't change the jar

what the checkout should be doing is setting your classpath so asking for that file gives you a path to the file on disk, and it's not doing that

I created a checkout dir and in there I ran ln -s ~/Projects/my-dep

Shouldn't that have set it up?

oh wait, lein now has built in checkouts separate from that plugin...

so the symbolic link should have worked (after just one initial restart)

@mario.cordova.862 one gotcha, the magic dir is checkouts not checkout

https://github.com/technomancy/leiningen/blob/master/doc/TUTORIAL.md#checkout-dependencies

I did create the checkouts with the write name, made a typo up there

and you restarted the repl at least once since adding the link in checkouts? if so I can't tell you what the issue might be

another gotcha is that this checkouts scheme only works for other lein projects

Yea the dependency is a lein project as well

Hmm going to keep searching, thanks though appreciate the help!

Figured it out

It was the way I was starting my repl

damn I was just about to chip in ahahaha

> Make sure not to override the `base` profile while using checkouts. In practice that usually means using `lein with-profile +foo run` rather than `lein with-profile foo run`

is it possible to use with-redefs to wrap a function? that is, can I refer to the original function that is being replaced, from the function I am replacing it with?

Yep, just store a reference to the original function in a let. I would give an example but clojure + phone = not good.

gotcha, that's enough to go on. thanks 🙂

alter-var-root is a thing too

if you refer to a var by name in a function, it's resolved at runtime each time it's used, by using a different name in a let, you "capture" the value at one point in the execution