Anyone have experience sending a file to download in compojure?

Is it possible for a user to submit a file via POST, the server does stuff to the file, then returns the changed file all in one swoop?

I've done image upload via compojure before, but I haven't had much experience with returning the changed file in the same operation

Though I suggest taking a look at output-stream to do the returning part

Good morning. I try to solve the last exercise of the do-things of the brave book : http://www.braveclojure.com/do-things/ . To solve this one. Do I need to change the symmetrize-body-parts or the matching-part function ?

Second question : Why do I see this error : CompilerException java.lang.IllegalArgumentException: Don't know how to create ISeq from: java.lang.Long, compiling:(C:/Users/rwobb/IdeaProjects/clojure-exercises/src/clojure_exercises/core.clj:12:1) on this code :

(defn my_intersection
  [set1 set2]
  (reduce (fn[acc item] (if (contains? set2 item) (conj acc item) acc)) {} set1 )
)


(my_intersection #{0 1 2 3} #{2 3 4 5})

Not sure, but don't you want to return a set, so the 'seed' for your reduce should be #{} rather than {}.

Yeah I just tested and that fixes it. Apart from that small error I think you nailed it! Gives the answer #{3 2}

So, when I use partition without supplying step I should get a sequences of lists containing n items each as I specified in n... If I want to check if the count of each list in that sequence is equal to a number, should I use map or apply

That sounds right to me. Your last one may have less in it or some may be left off I can't remember, I always look up https://clojuredocs.org/clojure.core/partition, then check its variants, to get what I want.

Well, partition when not supplying a step will drop the last set if it does not form a full partition

Yep, so you know what your count result will be

n

@cjmurphy: thanks, you are my hero

anyone who wants to help me to solve the last exercise of the do-things of the brave book

it's this challenge : https://www.refheap.com/112511

I only do 4clojure. ®️

pity. I wonder to solve this I have to change the symmetrize function or also the parts function

@cjmurphy: I do both to get a better feeling of the fp way of solving things

I need all my brain space right now for 96 on 4clojure. The last few easy ones are pretty hard. Maybe I'll still be at it by the time you catch up to me, and then you can give me a hand...

@cjmurphy: yep, the last one are pretty hard

For me there are not "easy" ones

the next I have to do is re-implement iterate

You can tell they are not that easy when not so many people have completed them, yet they have a low number.

for me there are not because I have trouble to solve them

You got that reduce pretty well, and reduce is pretty difficult when you first see it.

thanks, I had lots of help here to find out what the right syntax is for reduce

I try to do every day 1 or 2 challenges of 4clojure

I hope someone else can help me

I can wait

@cjmurphy: which one is 96?

For this one (http://www.4clojure.com/problem/62) Can I use loop - recur. Then if so, then I have to think how to stop the loop

96 is "Beauty is Symmetry"

This one : http://www.4clojure.com/problem/96

That's a smart way of finding out!

If only I was more webby!

try it but if Im wrong I have a function which works till infinity and a computer which will be slower and slower 😞

more webby ??

more knowledgeable about the web, I think he means

oke, thanks

I get the feeling that the remark of @cjmurphy was not intented to answer my question ?

Um - affirmative, that one, 96.

For this one (http://www.4clojure.com/problem/62) Can I use loop - recur. Then if so, then I have to think how to stop the loop

Which you do by wrapping it with lazy-seq, which means nothing will happen unless you force it out, with something like a take.

So do it exactly the way you are thinking, then (lazy-seq it)

i.e. lazy-seq it!

@cjmurphy: oke, time to hit the manuals to learn more about lazy-seq

thanks again

Conceptually very interesting the whole laziness thing. Not exactly easy to think about, but possible to get results with regardless.

Actually even map is lazy, so we use laziness all the time.

This is a whole new concept for me

oke, I know map but never knew it was lazy

clojure makes me learn every day new things

I actually think that here is the best place for questions about 'exercises in the Brave book'. If people want to help they join this beginners channel.

oke

lazy~

Laziness in Clojure is a pain point, IMO. 99% of the time everything just works and you don't even notice what parts are lazy and what parts aren't, and then every once in a while you get an error because of it, and those errors seem cryptic for quite a while after you start working w/ Clojure.

In some ways it'd be easier if the language were either consistently eager or consistently lazy. It's one of the few complaints I have about the language.

So @roelof it's not just you 😉

I know it not just me

already someone who wants can help me with my brave problem ?

Sorry, I shall slep

good night then , @trancehime

Why do I get this error message : ArityException Wrong number of args (0) passed to: core/eval1476/fn--1477 clojure.lang.AFn.throwArity (AFn.java:429) on this code :

(defn roelof
  [function number]
  (lazy-seq (cons number(function) )
  ))

(take 5 (roelof #(* 2 %) 1)) 

You need a space between number and (function) would be my guess

Nope, that's not it. I never realized that didn't matter in Clojure at all

The issue is that you're calling function

With no arguments

But the function you passed in #(* 2 %)

Takes an argument (represented by %)

oke, the argument is number if I understand everything well ? @surreal.analysis

I think so, but I'm not positive what you're trying to do. What do you expect the result of the last statement to be?

Because cons also takes 2 arguments, but if you move number it will only take 1. It also needs a base collection

I try to solve this challenge : http://www.4clojure.com/problem/62

As it takes an element and a collection

@surreal.analysis: then I have to think good what the collection is

Yes

I think the issue is you likely want some recursion

I think so, that why im using lazy-seq

Right, but you want to call the roelof function from inside roelof

oke, back to the manual to read more about lazy-seq

@surreal.analysis: so more a function like this :

(defn sum-last-2 
   ([] (sum-last-2 1 2)) 
   ([n m] (cons n (lazy-seq (sum-last-2 m (+ n m))))))
 

Yes, pretty similar, but you shouldn't need the 0 arguments option, and you need to replace the m (+ n m) part with your code

Oke, thanks, I know then Im on the right track now

hmm, still a problem : I have now this (cons number (lazy-seq (my-iterate number (function number))) but see this error message : ClassCastException java.lang.Long cannot be cast to clojure.lang.IFn

and when I do (cons number (lazy-seq (my-iterate function number)))) the function does not get executed I see as output { 1 1 1 1 1 }

think I found it after looking good at the examples

and solved

🙌

blush blush

now hope someone can help me with my brave problem and I solved the number of exercises I want on a day

whats the brave problem?

exercise 6 of the do-things chapter. See here :

6.Create a function that generalizes  symmetrize-body-parts  and the function you created in Exercise 5. The new function should take a collection of body parts and the number of matching body parts to add

the functions can be found here : https://www.refheap.com/112518

I wonder which function I have to change for it

@cab : is my problem clear ?

which function did you make in Exercise 5?

matching-part?

nope, I changed symmetrize-body parts

ah

let me open http://www.braveclojure.com/do-things/ 😛

I changed this

(set [part (matching-part part))

(set [part (matching-part part "right1-")
                                         (matching-part part "right2-")
                                         (matching-part part "right3-")
                                         (matching-part part "right4-")
                                         (matching-part part "right5-") 

right

so you want to generalize that — make it so it accepts any number of parts

and

{:name (clojure.string/replace (:name part) #"^left-"  "right-")  

{:name (clojure.string/replace (:name part) #"^left-" replacement) 

do you know what you want to do conceptually?

@cab : I believe that is what the exercise wants

I think I change the multiple parts to one call and use something like repeatly

yeah

I only do know if that is the right way

and if you can make the output like left-arm1

@cab that is why I asked the experts for help

anyone here ??

This is not working

(into final-body-parts (set [part ( repeatedly (matching-part part "right1-") number)
                                 ]))) 

Then I see this error message : clojure.lang.PersistentArrayMap cannot be cast to java.lang.Number

and I cannot change the replacent part to things like right- 1- / right-2-

@roelof: hmmm. are you trying to do set! or make a set out of a vector with part?

or maybe a let?

no, im trying to solve a exercise of the brave book where I ,must generalize a function so it works on a given number and not on a fixed number

which excercise?

exercise 6 of the do-things chapter

I have to generilaze this function : https://www.refheap.com/112520

Here is one hint: (map #(str %1 "-") (range 1 n)) to change up how you have the symmetric thing in there.

Something like that: https://www.refheap.com/112523

@roelof:

@base698: it this part right ;

(defn symmetrize-body-parts
  "Expects a seq of maps that have a :name and :size"
  ([asym-body-parts] (symmetrize-body-parts asym-body-parts 2))
  ([asym-body-parts n]

why 2 functions with the same name

so it can take the optional number. You can call it like (symmetrize-body-parts parts-list) or (symmetrize-body-parts parts-list 5)

oke, but here you set already a number :

symmetrize-body-parts asym-body-parts 2 

yeah, that's the default case when you call it like that it does 2 (mimicing left/right)

instead of left right it's 1/2

i'll leave that to you to figure out

oke. thanks

oke, it works also without the optional number and then it looks like this : https://www.refheap.com/112526

but now the output looks like this :

{:name "left-eye", :size 1}
 {:name "2-eye", :size 1}
 {:name "1-eye", :size 1} 

What do I have to change to make it work like this :

{:name "eye1", :size 1}
 {:name "eye2", :size 1}
 {:name "eye3", :size 1} 

the matching part function looks like this :

(defn matching-part
  [part replacement]
  {:name (clojure.string/replace (:name part) #"^left-" replacement)
   :size (:size part)})

I hope anyone can help me ?

just swap the str part

and matching