hi

wha’ts the (num) function used for?

if its purpose is to coerce to a number, then why (num “333”) fails?

It coerces to a clojure.lang.Number

It doesn't parse a string into one

@didibus could you name an argument that is not a number but `num’ accepts?

(int 333)

@i change your comment to "is not a clojure.lang.Number" and it should change your perspective.

It's a super niche function that you probably don't need

@didibus still i don’t know what it does. for example, (num 333), however, 333 is already a number.

333 is read as a number by the reader

But if you cast it to an Integer with (int 333)

And then want it back as a Number, you can use num back on it

Honestly, I have no idea when or why this use case would come up

But basically all the number coercion functions coerce from one to the other

They don't coerce from non Number types

Which is why (int "333") also doesn't work

You need to use either Java interop and the Parse methods to do so, or use the reader itself.

i see. Number is the base class of Integer, Long, etc. so basically its using the base class Number as abstraction. Very java-ish, oo flavor.

It basically takes from any more concrete type, like float, int, double, long, etc. And coerce it back to the Clojure default for the number

Like how the reader does it

I think you would use it like if you write a number operation

And for the operation, maybe you had to coerce numbers, but you want to return it back to the appropriate Number type

Then before returning, you'd call number back on it

Also, it seems it just. Basically boxes a primitive number to its object variant

I'm looking at the source now

So long becomes Long, int becomes Long, double becomes Double, float becomes Float

And everything else become java.lang.Number

Which mostly mean they stay the same

So BigInt will remain BigInt. Etc.

Bottom line, probably not what you want. Try: (Long/parseLong "333") instead.

There's also Float/parseFloat and same for Double, Integer, etc.

If you don't want to specify the type to parse into, and want the same logic as Clojure litteral syntax, you can use (edn/read-string "333")

It if you trust the input string, you can use Clojure's read-string as well

@didibus still a little bit confused. (type (num 1)) gives long, not number.

(def a 3) (def b (num a)) (identical? a b ) ==> true

what’s (type (int 1)) and (identical? (int 1) (num 1))?

i feel the doc may be little misleading.

(num) says, `coerce to a Number’.

This a relevant issue: https://clojure.atlassian.net/browse/CLJ-2451 — it’s something that confuses a lot of people

@i It doesn't say "coerce to a Number", it says "coerce to Number". That's an important difference.

@seancorfield what’s the Number here? the java.lang.Number ?

But you'll almost never find a use for num. Primitives are automatically boxed in Clojure, which means they end up as Long or Double most of the time already. And those are java.lang.Number.

(num (int 1)) creates a java.lnag.Long. but (int 1) is already a Number (Integer)

Yes, exactly.

(number? (int 1)) ==> true. and (num (int 1)) still coerces. that confuses me.

num on a float (primitive) will produce a Float (`Number`). num on a double (primitive) will produce a Double (`Number`). That's all it does.

The entire implementation: https://github.com/clojure/clojure/blob/master/src/jvm/clojure/lang/Numbers.java#L1479-L1489

Yes, it is "java.lang.Number"

java.lang.Float, java.lang.Integer, java.lang.Double, java.lang.Long are all children of java.lang.Number

About the only useful behavior of num is that it throws an exception when called on something that isn't a Number 🙂

Clojure will coerce to the most specific children

So primitive type long (no uppercase), will coerce to java.lang.Long, which is a child of java.lang.Number

I suspect num is mostly used by Clojure itelf, as the implementation for the auto-boxing Sean mentioned, but I can't confirm

Well, there are lots of calls to the static method num() inside clojure.lang.Numbers.

i am little bit lost in the conversation. given your code snippet, of `return (Number) x’. I wonder what happened when (type (num (int 1)) becomes Long instead of Integer.

@seancorfield

Because (int 1) is autoboxed to Long, and Long is already Number so the cast does nothing.

Like I said, pretty much the only useful behavior of num is that it will throw an exception if called on something that isn't a Number.

I would imagine that it is almost never used in production code.

(and if http://crossclj.info still existed, we might be able to answer that to some degree!)

(type (int 1)) ==> java.lang.Integer

@seancorfield i mean, it is boxed to Integer not Long.

Sorry, I meant Integer there.

user=> (type (int 1))
java.lang.Integer

Ya, I'm not sure about that part either

(...and Integer is already Number so the cast does nothing)

In Java, casting an Integer to Number returns an Integer

So this is confusing:

user=> (type (num (int 2)))
java.lang.Long
user=> (type (int 2))
java.lang.Integer
user=> 

And the implementation is commented out: https://github.com/clojure/clojure/blob/master/src/jvm/clojure/lang/Numbers.java#L1579-L1581

But that wouldn't be invoked anyway: (int 2) is already boxed to Integer by that point.

So it would go through the Object case and be cast to Number.

Ya, and that cast should not coerce to Long

user=> (type (cast java.lang.Number (int 1)))
java.lang.Integer

Its weird though:

user=> (type (identity (int 3)))
java.lang.Integer

But meg

meh

This is a rabbit whole I'm afraid

user=> (type (num (double 1.0)))
java.lang.Double
user=> (type (num (float 1.0)))
java.lang.Float
user=> (type (num (short 1)))
java.lang.Long
user=> (type (num (byte 1)))
java.lang.Long
user=> 

Hum.. maybe. But there is an overload for num(long) and num(float) respectively which coerces them to that.

For int, there isn't, so Clojure first auto-boxes it into something, and calls num(Object) with it,which just returns it casted to Number

Maybe, type has an overload as well 😛

Ah, I'd missed the long overload. That explains it: in Java, byte, short, and int will all coerce to long first -- so that's the overload that processes all of them.

Oh does it now

The five definitions of num() are not together.

I only saw the first three... doh!

I didn't know Java did that

Well, four since the int overload is commented out.

Now it makes sense.

So java will favor the long overload given an int?

If there are no int overload ?

Yeah.

Interesting, well that explains it

Got that @i?

Clojure will call num with primitive type int, and Java will coerce it to primitive long, and dispatch to the primitive long num overload, which will coerce it to a boxed Long.

(! 686)-> cat Promote.java 
public class Promote {
public String foo(long x) { return "Long"; }
public String foo(short x) { return "Short"; }
public static void main(String[] args) {
	Promote p = new Promote();
	System.out.println( p.foo( (byte)1 ) );
	System.out.println( p.foo( (short)1 ) );
	System.out.println( p.foo( (int)1 ) );
	System.out.println( p.foo( (long)1 ) );
	System.out.println( p.foo( 1 ) );
}
}

Mon Jun 10 22:58:56
(sean)-(jobs:0)-(~/java)
(! 687)-> java Promote
Short
Short
Long
Long
Long

I guess it picks the best type that can fit

if you remove the short overload, does byte and short now go to long ?

Yes.

Also, haha, ya, I've been writing so much Clojure, when I need to do a Java code review or code change, I'm like.. what the hell is this mess! 😛

Clojure is spoiling me actually

That's the biggest downside of it 😮

You can never go back and be happy

I've written almost zero Java in nine years at this point...

Wow, that's crazy though! I still deal with a lot of mixed Java/Clojure project, but slowly Clojure is taking over

Work was a CFML (ColdFusion) shop when I joined!

My partner was going through interviews recently though. And as I was helping her practice some interview questions, I realized... damn, you can't do an interview question in Clojure 😛 And I was trying to get back to using Java and I kept being like.. Where are the functions I need!

I tried to introduce Scala but that didn't suit the other team members. So I tried Clojure, and that did.

So we slowly switched from CFML to Clojure, trading one dynamically compiled JVM language for another 🙂

Also people are like... Given an ArrayList... can you modify it in place. And you're like... You mean HashArrayMapTrie 😉

Oh ya, you told me CFML's latest versions were actually JVM based

Consequently, our CFML code contains stuff like this in a few places:

var cols = clj.clojure.string.join(
            ",",
            core.map(
                core._name(),
                core.keys( core.first( items ) )
            )
        );

That's pretty cool that you can do Clojure interop from CFML

(the weird _...() syntax just gets a Var reference)

Heh... Late Night with Clojure, very interesting episode tonight!

We have people using Clojure libs from Java and Scala. Clojure is really easy to use from other JVM languages, its a great strenght

Our entire process for the last eight years has been based on CFML/Clojure interop. But we've retired our biggest CFML app now.

I've run a Clojure REPL in a Scala microservice.

Ya, its one way though... Scala from Clojure is not that easy

That's why you should move from "other jvm lang" to clojure only 😛

Can't imagine a reason to try, either. Or rather, can't think of anything I'd want to use from Scala in Clojure

Yeah, we have a live Socket REPL in our last remaining CFML app 🙂

The CFML/Clojure "magic sauce" https://github.com/framework-one/cfmljure

(I just pushed the latest cfmljure.cfc from our work codebase but the rest of the repo is about two years out of date)

So, when using CFML, do you still use the ColdFusion IDE ?

@didibus Hahaha nope. I used Emacs for a few years, then Atom.

@deleted-user Look at clojure.java.shell I think

Ya, clojure.java.sh is great

super easy

http://clojure.github.io/clojure/clojure.java.shell-api.html#clojure.java.shell/sh

Just make sure you call System/exit or shutdown-agents when done

Or your program will take an extra minute to quit

Ya, I think it can do that

Otherwise what's the point of using agents

But I never tried, so maybe not 😮

No, clojure.java.shell/sh assumes the process ends.

So you'll probably have to use Java interop and some standard Java libraries?

java.lang.ProcessBuilder is probably what you want.

java.lang.Process lets you get an OutputStream which you could read as it becomes available.

https://github.com/clj-commons/conch

Could be you can just modify the impl of sh: https://github.com/clojure/clojure/blob/fe0cfc71e6ec7b546066188c555b01dae0e368e8/src/clj/clojure/java/shell.clj#L110-L128

Lets you get program output as a lazy sequence of lines.

It seems it returns stream, but I'm not 100%

Just use Conch 🙂

I wasn't sure if it had been forked into clj-commons, so I had to go check.

(and with that, my work here is done... time for bed!)

Yeah, pretty much anything in Clojure that uses concurrency will require (shutdown-agents) or an explicit (System/exit n) call.

gn

@didibus i see. i didn’t notice the java overloads.

Wow, joker is pretty neat for quick scripts

beyond a linter

If I want to read the implementation of the thread macros where would I normally go look for that? (I'm less interested in the code than I am the skills to go find those sorts of answers myself in the future) ^_^

(source ->) could be handy 🙂

❤️ ❗

and try expanding examples (clojure.pprint/pprint (macroexpand '(-> {} (assoc :a 1) keys first val)))

I really need to pick up the habit of using the repl analysis tools more in general I'm finding. ^_^

is it always possible to turn a recursive function into a tail recursive function?

Possibly wrong question, but I am very much out of the loop. How safe is to use the python version of the transit library, in production? It seems quite abandoned but I know that can be misleading…

I am pretty sure the answer is no, although there might be some pretty wild contortions or modifications to a program that theoretically make it possible. The kind of example function that I do not see a clean way to turn into a tail recursive function is one like Clojure's tree-walk, or in general anything where the return value is the result of two or more different recursive calls.

So I finally understand the difference between -> and as-> when expanded, with -> nesting forms and as-> setting up a let with each step. My question is, why do they do it differently? Is there some trade off between the two approaches? Or are those transparent to the compiler?

They both have the same result.

lets are mostly immaterial in the compiled code, using lets in as-> leads to a simpler implementation

So, seeking to achieve deeper enlightenment on quoting and macros, I thought to build my own. But I can't seem to understand how a symbol is getting resolved...

1 (defn-                                                                                                                                                                
  2   placeholder
  3   "put __ in as first arg if none present"
  4   [form]
  5   (conj (rest form) '__ (first form))) ;;if not yet written...
  6   
  7 (defmacro =>
  8   [expr & forms]
  9   (let [new-forms (map placeholder forms)]
 10   `(let [__ ~expr
 11          ~@(interleave (repeat '__) (butlast new-forms))]
 12      ~(if (empty? new-forms)
 13         name
 14         (last new-forms)))))

the ` on line 10 turns into a namespaced form, but the code on line 11 should be OK

Is there a way to avoid it namespacing it?

the usual idiom is

~'__

So really what I was missing there was the differences between backtick and quote

?

Quote disables symbol substitution for a form. Backtick is similar, but also replaces plain symbols with fully namespaced symbols (e.g. "filter" => "clojure.core/filter")

(as well as allowing unquoting / splicing)

For my favorite version of the threading macros, see https://github.com/cloojure/tupelo#literate-threading-macro

And the source code: https://github.com/cloojure/tupelo/blob/master/src/cljc/tupelo/core.cljc#L1322

it-> is just as-> with the symbol name fixed to it

(as-> 1 it 
      (inc it)
      (+ it 3)
      (/ 10 it))

but I hate the "backwards" nature of as-> . 😞

It's mostly designed to be used in -> pipeline

yeah, all the arrow macros are designed so -> can be their parent, and you can mix them

(-> 1
    (inc)
    (+ 3)
    (as-> it (/ 10 it)))

I mean, I made a version that's a knock off of ramda's, not sure if that's good but I'm all kindsa tickled to have made it work.

what are people's thoughts on using datafy to parse java object models into data representations for returning back via an api

for example i'm playing around with something like that for the google maps java lib:

(extend-type DirectionsLeg
  p/Datafiable
  (datafy [this]
    {:arrival-time (.arrivalTime this)
     :departure-time (.departureTime this)
     :distance (.inMeters (.distance this))
     :duration (.inSeconds (.duration this))
     :duration-in-traffic (.durationInTraffic this)
     :end-address (.endAddress this)
     :end-location (LatLng->vec (.endLocation this))
     :start-address (.startAddress this)
     :start-location (LatLng->vec (.startLocation this))}))

(extend-type DirectionsRoute
  p/Datafiable
  (datafy [this]
    {; ignoring until we need to draw things
     ;:bounds (.bounds route)
     :copyrights (.copyrights this)
     ;:fare (process-fare (.fare route))
     :fare (.fare this)
     :legs (map datafy (.legs this))
     ; ignoring until we need this to draw things
     ;:polyline (.overviewPolyline route)
     :summary (.summary this)
     :warnings (.warnings this)
     :waypoint-order (.waypointOrder this)}))

(extend-type GeocodedWaypoint
  p/Datafiable
  (datafy [this]
    {:partial-match (.partialMatch this)
     :place-id (.placeId this)
     :address-types (map str (.types this))
     :status (str (.geocoderStatus this))}))

(extend-type DirectionsResult
  p/Datafiable
  (datafy [this]
    {:waypoints (map datafy (.geocodedWaypoints this))
     :routes (map datafy (.routes this))}))

previously i just had processing functions that did the same thing. i like this better because its immediately clear what java object something is operating on where as before that would only be clear if you added type hints

but i suppose there's the chance for causing some confusion by making third party objects datafiable

but this is just internal application code not a library so seems lowish risk

seems fine. you probably want to type hint this or you're using reflection for all of that

seems fine as in its not totally bonkers or seems fine as in that could be a reasonably common pattern 🙂

seems like a common thing already being done in many places to translate from Java objects to Clojure data. might as well do it under the datafy protocol

don't extend Datafiable to things not under your control in a library

you can extend it to whatever if you're building an application

extending to com.foo.geo.GeocodedWaypoint is fine if your library pulls in and owns all interaction with com.foo.geo

also shouldn't extend Datafiable to platform things like java.time.LocalDate

you can always duplicate the protocol under a different name if you need to extend it to things you don't own

yeah doing it in a library sounds like a recipe for confusion

I've written Datafiable a bunch of times under the name IShredJava with a single method shred

\m/

@alexmiller just as an fyi, the docs say that extend-type automatically adds the type hints to 'this' for me

oh someone already said that in a thread, whoops

well then nvm! :) I forgot that

Hello guys, I don’t know if this is the right place to ask for an opinion on my case here, but anyway: Me and 2 friends started on the beginning of this year to study together, Design, Front-End and Back. I’m on the back with clojure... And we have finished a small web app that downloads musics and playlists from YouTube. Now, we are going to start a second project, but here’s the thing, I need to build an app which will be scalable, fully tested and ready for production, including DevOps tools and best practices. But this app needs to serve two purposes: first it needs to be something that we can use as an example of an app built by us, to show to possible clients in the future (so they won’t think we are starting out of nowhere) and this needs also to be something I can use myself to show if I need in the future a regular job with clojure. (Btw I’m going to document every bit of this project on a personal blog with daily posts, with videos too, to show my Learning path along the way.) So, we don’t know what kind of clients we can come across on the future (likely that will be small systems using web clients, small because it’s only me at the back end for now) but we don’t know what kind of system we would need to build, so the web app we are going to create now, should be something that suffices as a real world example and that also gives us more knowledge for the upcoming future. What you would suggest for us to build? What kind of app? Would any kind be enough for this? I have some ideas but I’m not sure if will be enough to show off...

can someone here help illuminate me as to why emitUnboxed might get called instead of emit on a StaticMethodExpr? I’m assuming it has something to do with the method signature?

In Compiler.java

if the method is called in a position that allows for primitive return, then you'll get emitUnboxed

It seems that both emit & emitUnboxed get called during compilation for the method in question

When you say “in a position”, you mean e.g. (if (MyClass/myMethod ...) ...)

yes

or (.method inst (.othermethod inst)) for example

vs. (fn [& args] (MyClass/myMethod ...))

yes, or (identity (.method inst))

Thanks, that’s helpful!

if you are chasing down some problem and haven't turned on reflection warnings I would suggest starting there instead of digging through the compiler

We fail compilation on any reflection warnings 🙂

You should see the gratuitous type hints in our code

😞

It’s the life of Java -> Clojure -> Java unfortunately….

you can look for canEmitPrimitive impls in Compiler.java for all the paths where emitUnboxed can be used

I’m mucking around in the compiler because I’m getting IncompatibleClassChangeErrors saying Method {myMethod} must be InterfaceMethodref constant

Calling this method in my REPL works just fine… but calling the function in our code with that method in my REPL on JDK 11 throws that error

It looks to me like this test should trigged the emitUnboxed code path? - must be InterfaceMethodref constant

Whoops

This test - https://github.com/clojure/clojure/commit/3d6c1364698a4b7020a6d97f33b9a596a1160d4b#diff-c457bcb7e510777c5e80c12f5f9362bcR434

Haha oh man. I fixed the error. Hallelujah

Anyone that’s a contributor want to submit a patch for me? Lol

not sure what you mean, in that tast the result of the method calls are then passed to a function =, so not emitUnboxed

yeah that makes sense

There’s a bug in emitUnboxed

for StaticMethodExprs

sorry, reverse that

double reverse it

For some reason I thought = was a built-in form like if…

I’m not sure why

if doesn't cause emitUnboxed either, because it has to handle anything (Object), true, false, and nil

if will sometimes result in emitUnboxed being called if the test can emit a primitive boolean

Well, I can reproduce by putting this method as a condition to if. It will spit out this error at runtime

I changed the code in emitUnboxed and now if works properly

what's the diff?

my guess is you are running with slightly different versions of some class at runtime and at compile time

Compiler.java line 1802

gen.invokeStatic(type, m); -> gen.visitMethodInsn(INVOKESTATIC, type.getInternalName(), methodName, m.getDescriptor(), c.isInterface());

It’s the same fix that was applied to emit for this class

let me see if I can break Clojure’s unit tests

makes sense

I can repro on the unit test too

oof, this took me longer to figure out than I’d like to admit

I thought it was an issue in clojure-maven-plugin for so long

@ghadi ^

I can make a ticket + patch for you if you want, but registering for a CA should be easy nowadays if you want to do it yourself

Honestly not sure if my company would let me contribute even if I asked nicely

I can get a diff together though with a unit test

it's ok I'm on it

thanks for finding out about it

For the unit test, I just added -

nevermind looks like I can't login to the new jira 🙃

And -

That last case breaks w/out the patch to Compiler.java

https://clojure.atlassian.net/browse/CLJ-2517

I think this line needs to be staticMethod2? -

+    (is (= 1 (if (compilation.JDK8InterfaceMethods/staticMethod0 true) 1 2)))))

Thanks for doing that 🙂 much appreciated!

so it does, it's a bit too late for doing this :) thanks

no problem!

LGTM, thanks @bronsa 🙂