hello guys, am using figwheel to start my ring handler with the :ring-handler option, however was wondering if there is a way to start something like a scheduler on application start up when using figwheel, something like :ring {:init xxx } for the ring plugin

or if there is a cleaner way to start a scheduler on application start up

http://clojure.org/about/spec#_don_t_further_add_to_overload_the_reified_namespaces_of_clojure do these things have to be explicitly kept in mind when using spec or does it fall naturally out of its API/nature?

in your experience

@nikki: that particular section is justification for why spec is implemented the way it is -- not something that affects how you use it.

I'm trying to understand how to write a spec generator

what I want is a custom generator for DNA sequences.

`(gen/elements (seq "ACGT")) seems part of this. But not sure how to make the composition to generate strings (as a generator)

@seancorfield: neat! and is the idea that by using spec it solves some of those problems 'for free'?

without adding accidental complexity

Hi I am trying to run a long running method And i want to track it via jmx the code i currently wrote looks like this

(defn- start-long-running-method []
  (let [start-ts (ts/now)]
       (jmx/register-mbean
        (jmx/create-bean (ref {:time-elapsed (- (ts/now) start-ts)}))
        "my.namespace:name=Foo")
       (start-long-running-method)))

oh, this works: (gen/sample (gen/fmap clojure.string/join (gen/vector (gen/elements (seq "ACGT")))))

wondering if an editor could use clojure.spec specs to generate local UIs for editing sexps -- like a color picker for the color field -- if you are using something like 'lisping' for editing clojure https://www.youtube.com/watch?v=nHh00VPT7L4

(i think clojurescript over react-native is probs best suited for the UI rendering bit)

Exists a library which helps to communicate over unix sockets?

@danielgrosse Hi 🙂 There’s manifold/aleph, which talk to netty. I don’t think they do UNIX sockets right now, but netty does.

@danielgrosse If you want low-level bindings, there’s always jnr-unixsocket

(I would strongly recommend looking at aleph and netty)

Trivia question: for an xs with 10 elements, when is (get xs 3) not equivalent to (nth xs 3)?

@pesterhazy xs = [] for example

[] doesn't have 10 elements

pesterhazy: seqs?

I'll read the question properly next time! 🙂

@lvh, 💲

yay

curiously (get (seq [:a :b :c :d]) 3) returns nil

yep

at least it’s consistent I guess?

pesterhazy: since it was trivia time, you know why it’s nil right

nihil, latin for nothing?

well

yes

but

(get '(1 2 3) 1 ::not-nil)

(the real reason is about if it’s an IAssoc or not)

a vec is, and a seq is not

(at least not generally)

I guess it would be fine if get threw if applied to a non-associative coll

as it is it's a head scratcher

you change [:a :b] to (map identity [:a :b]) somewhere and ... suddenly nil

vectors and seqs aren’t the same kind of thing in my head, so I haven’t really had that problem as much

(it’s pretty rare that I call nth)

I've developed that mental distinction too

seq[able]s are generic "collections", that have ordering if you need it

intentional vectors are very specialized

and I never conj onto a seq so I don't have that problem either

right

I treat a vec like a seqable reasonably often but then it’s no longer ok to call get on it

typically: I want to reify a lazy seq

what does that mean?

like, unlazy

you mean that's your typical use for a vector?

maybe not the typical use case, but it happens, yeah

but then it’s just an eager seq(able)

right

my idea so far was, nth is not very useful because it throws on index out of bounds, so I should just use get instead

guess that's not good advice unless I know I'm dealing with a vector

throwing is useful sometimes too

Anyone here familiar with Amazonica? I’m trying it, and evaling (#'amazonica.aws.ec2/describe-vpc-attribute :vpc-id "vpc-xyzzy" :attribute “EnableDnsHostnames”) gets me com.amazonaws.services.ec2.model.AmazonEC2Exception: Value (EnableDnsHostnames) for parameter attribute is invalid. Unknown attribute. (Service: AmazonEC2; Status Code: 400; Error Code: InvalidParameterValue; Request ID: iddqd). From the Javadoc and examples I was expecting that to work....

does anyone of you use Bamboo with Leiningen to build and deploy jars?

I can't get jar versioning right...

Is there any reason a component's (stop [this] ...) function wouldn't be able to (get this :something-i-assoced-as-the-final-expr-of-start)?

I thought that was kind of the whole point of component, but I must be Doing It Wrong™

@pandeiro Yes. Idempotency is a part of component. You should be able to call stop multiple times.

https://github.com/stuartsierra/component#idempotence

idempotence is kind of ambiguous here

@dominicm OK I can write conditional logic for that, but that's not the issue

the issue is, the thing I assoc'd isn't there

Not even on the first call of stop

Following a start, you mean?

Yes

pandeiro: are you calling stop on the object you originally called start on, or the return value from start?

Ah, I misunderstood the question then.

gfredericks: ahhh

Which should it be?

the latter

this is my least favorite thing about component

yikes

fun stuff!

it's a weeeird ambiguous mix of immutability and statefulness

@gfredericks Do you have an alternative approach you use in some situations?

nope

the only other idea that comes to mind is just traditional OOP objects

which I haven't tried

I've never run into a case where I'm interacting with the components this directly. Mostly I use the example copy/paste from component or the reloaded.repl one. Why are you doing this directly, out of interest?

I am building my application at the REPL 🙂

So I did (def system (start-my-system)), then (component/start system), and then silly me, (component/stop system)

the irony being that in trying to figure this out, I have restarted my REPL dozens of times... not exactly the reloaded workflow I was hoping for

https://github.com/weavejester/reloaded.repl I would highly recommend just using this.

Thanks, I will eventually check that out but I'd like to limit the moving parts first to better understand what I'm doing

(as clearly I was not understanding component very well)

It's the stock https://github.com/stuartsierra/component#reloading example, packaged up so it doesn't get lost when doing a c.t.n/refresh.

The example in the README is good for understanding too ^^

Based on your examples, I think the distinction worth noting is that it should be init-my-system not start-my-system

Good point, @dominicm

Is there a reason for preferring (assoc this :item nil) to (dissoc this :item)?

@pandeiro So, :item should be a key on the record, during the init stage it would be nil, during the start stage it will be (state). If, during the stop stage, you dissoc :item, I believe it stops being a Record, and turns back into a hashmap

Well, that didn't work (returned the first result..)

Works in the REPL ¯\(ツ)/¯

It is not strictly necessary for Component stop methods to be idempotent, but many people find it convenient to design them that way.

@pandeiro It is common to have to restart the REPL a few times when developing / debugging your component implementations. I still have to do this myself on a new system. Once it's set up, the workflow gets smoother.

Appreciate the encouragement @stuartsierra, thanks

https://github.com/stuartsierra/reloaded is a Leiningen template with an example of how I set up a new project using Component.

How long should it take a complete newbie to get a bare bones full stack clojure application live? I wanted to put together a small talk for my company about clojure and i assume they would respond best to a working application. Which i tried to headstart using luminus: lein new luminus vending_machine +re-frame +datomic My plan was to immediately deploy that to heroku and make sure i could redeploy every step along the way. sadly i hit an unexpected error on the next step. ‘lien uberjar` leads to ...

Compiling "target/cljsbuild/public/js/app.js" failed.
Exception in thread "main" java.lang.NoSuchMethodError: com.google.common.base.CharMatcher.javaUpperCase()Lcom/google/common/base/CharMatcher;, compiling:(/private/var/folders/qx/mn5d4sjn7w5b4fxs2l15lzk80000gn/T/form-init612906228494054095.clj:1:124)

I'm looking for a general Clojure oauth2 library. It looks like there's a billion different such projects on GitHub or Clojars, few of which are both actively maintained, pushed to Clojars, and support Oauth2. Is there a go-to library for Clojure projects for this?

@drewverlee yeah, hard to tell why the compilation of cljs fails... One of the solutions is to assemble your project from the scratch, only using Luminus as an inspiration. To prevent dep conflicts earl on, add :pedantic? :abort to your project file.

@metametadata Thanks!. > One of the solutions is to assemble your project from the scratch, only using Luminus as an inspiration. Do you mean build just a luminus application then add :pedantic? :abort as a measure against dependency problems? then add re-frame and datomic as individual steps? I was sort of hoping that lein new luminus vending_machine +re-frame +datomic would just work 🙂

brb

I feel your pain! But I meant creating a totally empty Clojure project with pedantic setting and start adding stuff iteratively 🙂 It will take more time and figuring stuff out but you'll really understand all the code.

Maybe you could also try using the luminus template without "+re-frame" and add that part manually or use another profile for frontend (e.g. "+reagent"). Because it looks like only the frontend compilation is broken.

and you may also look at the Duct framework template as a starting point: https://github.com/duct-framework/duct

I don't know where else to ask this, but after making a few clojure projects I'm starting to gravitate towards a specific way of organizing my project sub directories. Rather than create sub directories for various aspects of the project, like documentation, source, resources, testing and so forth, I find it more intuitive to organize the project in a pipeline like fashion. I have a directory named pipeline, and it contains subdirectories 0, 1, 2, and so forth. In the 0 directory I have a cljs directory, in the 1 I have html, css, and javscript directories, in the 2 I have clj files and so forth. Basically, I ask myself "What depends on what?", come up with a linear order, and then that is the way I structure my pipeline directory. What do you think the weaknesses or tradeoffs of this approach are?

@drewverlee do you absolutely need luminus?

chestnut with the reagant template always works for me, and then you can add datomic and re-frame on top

@bcbradley I think if you could come up with names for those directories it would dramatically improve discoverability. what you're talking about sounds a little like the concept of "layering" more than "pipelining"

@owen, No there aren’t really any requirements. I’m trying to learn and put together a demo.

@bfabry I guess it is more like layering than pipelining

@bcbradley it would be interesting to apply this to your clojure code.

To see if it encourages you to write more pure functions, and decomplect the state from logic

I try to stay away from state entirely

normally if i must have state, I'll "push it off till the end"

well that sounds a little lazy, this is what I really mean: If you have a function that is supposed to have impure behavior, if its current value given an input is supposed to actually depend on past values (in other words, it takes the "past" as a hidden argument)

then what I typically do is make a function that represents the entire application (when possible), that has that behavior

then I implement that function using nothing but pure functions, potentially acting on some local state

that allows me to keep the statefulness out of the real "meat" of the application, and keeps the complexity of the application to as low a level as it can be from the perspective an outsider

in other words, if i have to have statefulness (impurity) i make sure that only one function has statefulness. Namely the function that represents the application itself. Every other function (obviously the application is going to be built out of smaller functions) is totally stateless.

Every app can be interpreted as a function from argument space to solution space. Sometimes its hard to coerce it though.

Is there a plugin or something like that for making pagination for a blog

@roelofw partition-all 😛

oke, but partition-all cannot display things like 1 2 3 4 and so on

so links which a user can click to go to that page

sure, that was a bit of a tongue in cheek comment 🙂

np

Can someone point me in the right direction to understand when test-fixtures are run? For example, after each deftest or after testing or after properties/for-all?

I think it runs after each test-var

@johnnyillinois the documentation for use-fixtures

which is defined only by the deftest

Documentation doesn't include all possible use cases

it is either before and after each test, or before and after each namespace of tests

it's never just before or after, it's surrounding

I was looking at this: https://github.com/clojure/clojure/blob/clojure-1.8.0/src/clj/clojure/test.clj#L707

Yeah, agreed on the surrounding

that has nothing to do with fixtures - that's for calling tests defined via metadata, which is a feature that is rarely if ever used

totally! the macro: deftest as part of the execution phase calls test-var (from my understanding)

it does?

sorry, the macro only defines a function which calls test-var

https://github.com/clojure/clojure/blob/clojure-1.8.0/src/clj/clojure/test.clj#L621

oh, funny

I didn't realize it was hooked up that way, but there we are

that's funny - must be a trick so that reloads are handled properly

crazy world!

I knew that the :test metadata was an optional way to define your tests, I didn't realize that deftest actually used that same mechanism (very counterintuitive)

@johnnyillinois - I think this code makes it clear what the fixtures do https://github.com/clojure/clojure/blob/clojure-1.8.0/src/clj/clojure/test.clj#L730

the once-fixtures are all composed, and called with a function that calls the each fixtures surrounding each test

(and the each fixtures are composed as well)

@noisesmith Awesome! thanks

it's the responsibility of the fixtures to make sure they call the testing function passed in

and they can do their thing before or after or both as they wish

and ideally they only call it once

lol, yes ideally

though I guess I could imagine someone making an argument for conditionally not running the tests or conditionally running them multiple times for performance metrics or something - though I would be unlikely to agree

#makes-sense

Is anyone run into this issue with database truncation and fixtures? Currently, fixtures do not run around clojure.test.check.properties/for-all so there can be duplicate entities generated without a surrounding database truncation. If you have a uniqueness constraint, this can cause a problem.

Anyone dealing with this? How are solving it?

Trivially, one can truncate the database inside the test execution (but that seems "dirty")

I'll put some example code

(deftest insertion-into-db-test
  (properties/for-all [entity entity-generator]
    (insert-into-db! entity) ; can violate uniqueness
    (is (in-db? entity)))

Your fixture should run for that deftest — just once around the whole test.

Agreed! I am wondering how people are doing database truncation under that implementation

Don’t do generative testing on things that involve mutation and external services?

Yup!

Any other ideas?

I mean, as a general principle. That’s just not safe in general.

Or truncate the DB, those are really your two options

truncate inside the for-all, it's not dirty, that's actually the way you should do it if you have some sort of mutable state

but it'll be slow, so try something different if you can.

What are you really testing here? Business logic? Or mutating the DB?

Yeah... those are the baseline fixes. I am wondering if there is something better.

When I'm working with Datomic, I'll use a in-memory DB to do testing like this and just throw it away inside the for-all.

Not really because the for-all has to do some sort of backtracking to shrink the failing case.

I’ve been opening a transaction and rolling it back at the end of the test

so the body of the for-all gets executed many times.

You shouldn’t need to test that a JDBC insert! works — you should consider what in your function you’re really trying to test.

The actual test is more like:

(deftest my-test
  (insert-into-db! entity)
  (is (expected-json? (app request)))

Agreed, boundaries!

I familiar with the argument for isolating unit testing from the database and other side effects

These are integration tests

thanks @nwjsmith

and everyone else!

So imo, this is a great way to test, and the way I prefer to do it, is there a way you can isolate your DB inside this test?

Either use a in-memory db like sqlite or some option where creating and deleting a DB dozens of times in a single test isn't that painful

sure! we can have a database abstraction function (or set of functions)

The thing I love about this sort of testing, is that you have a single invocation of insert-into-db!, but there's nothing stopping you later on from doing for-all [op (gen-ops ...)] and then you can test for combinations of commands that result in invalid state

Basically instead of testing a single command, you can test a session of dozens of commands.

Yeah, that is a powerful feature