Has anyone tried the LispCast Web Development videos?

I am particularly interested in developing a REST API, so I would like to dig more in ring’s handlers, compojure, security/authentication, etc., does anyone knows if those videos could be a good starting point?

i signed up for the monthly membership but havent watched any yet

@rcanepa: Collections, in Java, refers to a class hierarchy containing various interfaces & implementations of map/list/set/queue/deque. See https://docs.oracle.com/javase/tutorial/collections/

@cjwebb: here I am

Did you post the question in beginners?

@cjmurphy: here I am

nope, In #C03S1KBA2

but I can repost it here again ?

Yes please.

I have 2 refs which represent a account like cash or bank. Now I want to calculate the new amount of the accounts. A transaction could look like this [ { :account cash :withdraw 100} ] [ :account bank :deposit 100] } I know I have to use alter but how do I do it when everything step of a transaction is in a map. and the map could have more steps then 1 as my example have shown

or can I do something like this ( map (alter ....... ) withdraws) and the same for the deposits

I have never (hardly) dealt with refs, but I know they are just like a db commit.

Can't you just have one ref?

I could but then I have to rethink how I can take care the amount of a particular account

now I have one ref which holds the amount of cash and one ref which holds the amount of the bank

Even an atom would work as long as you did the whole change in the swap!

one atom whichs holds two values ??

You can hold the world in one atom.

oke, I thought a atom or ref is like this (def cash {:atom 100})

I do this for a financial app so I need transactions otherwise things will go wrong

till now I have this : https://www.refheap.com/112363

(def default-state {:my-lines {} :hover-pos nil :last-mouse-moment nil :labels-visible? false :in-sticky-time? false :labels [] :current-label nil}) (def state (atom default-state))

{ :accounts {:cash VAL :bank VAL}}

or something

and I have doubt for the best way to do the last step. Chancing the values of the refs

An atom can basically be whatever you need it to be

oke, learned another thing

See @trancehime's example. But VAL can really be anything, like [{:what ""}{:what nil}]

Yeah, the atom can be modeled to suit your needs.

Modifying the atom's contents can be done using swap!

oke Can I have transactions on atoms. I need to have that so if a transactions like [ { :account cash :withdraw 100} ] [ :account bank :deposit 100] } fails nothings has to happen

for example if you want to withdraw more then the amounts of cash

that's what swap! is for

(swap! your-atom your-function)

Only one swap! ever happens at a time.

oke, thanks for the help

I will try that senario and some others

okay good luck

thanks

Another question : I have a vector of maps like this [ {:arg1 test :arg2 test2}] Now I need to have the contents of arg1 and arg2 for another function. So I could use map to iterate over the vector and get the first element. So far so good. Then I need a anymous function which as far as I know needs 2 arguments. But the arguments are not known till the first element is chosen. I can named it "it" so I can do (get :arg1 it) but I see then that I need to have 2 arguments. How to solve this one ?

@eggsyntax: Thanks

@games: I am watching Web Development right now

@rcanepa: I stream here: https://www.livecoding.tv/sveri/ from time to time. I am happy to answer questions too if I can 😉

@roelof: Something like this could work: ((juxt :a :b) {:a 1 :b 2} yields [1 2]

oops missing close paren

You could also do (map {:a 1 :b 2} [:a :b]), which gives you the list (1 2)

@codonnell: thats a cool trick

I haven’t seen that before

how come stuff like map, filter return lazy-sequences?

I don’t see why that is necessary/advantageous?

If you don't want a lazy seq, you can use mapv. Lazy and non-lazy have their own advantages and disadvantages.

You can handle things like infinite sequences with lazy operations.

(list +) '(+)

how come (list +) returns (#object[clojure.core$_PLUS_ 0x4415ab68

but ‘(+) returns (+)

for that matter

(list 'foo 'bar)

'('foo ‘bar)

returns (foo bar) and ((quote foo) (quote bar)) respectively

Quoting stops the REPL from evaluatin what's inside. So the type of the + in '(+) is a symbol, while in (list +), the + is evaluated and becomes a function type.

oh cool

thank you

very helpful

you're welcome

@sveri: Cool!… I will check it for sure!!

I am fighting with a simple problem and I can’t find the problem. I am sure that I am missing some detail, can anyone take a look a this?. It is a simple handler that I created to learn about ring and compojure. For some reason, I can’t coerce a string (request parameters) to an Integer.

I am getting this error:

No implementation of method: :render of protocol: #'compojure.response/Renderable found for class: java.lang.Long

@rcanepa: I guess compojure expects something it can render as return value of "calc"

But it gets Long, thats where the error comes from

Btw. I start another stream in a few minutes, I can show you what I mean there, if you want

@sveri: Yeah… you are right… I wasn’t returning a response map.

Just a number!

exactly