Re: Trait-like behavior with Protocols

[Konrad Hinsen]

On 9 Feb 2010, at 22:29, aria42 wrote:


If this situation is common enough, shouldn't defprotocol support
optional implementations which are implicitly merged?


Yes, if it is common enough. It's perhaps too early to decide.

Konrad.

--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your 
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en

Re: clojure gen-class questions

[Meikel Brandmeyer]

Hi,

Am 09.02.2010 um 18:10 schrieb Аркадий Рост:

> Oh...So to make methods I must declare them in gen-class clause and if
> some function wasn't include in gen-class clause, it wouldn't be a
> method even if it had a prefix from gen-class clause.
> I mean:
> (ns example.class
>  (:gen-class
>   :prefix pre-
>   :methods [[method_name1 [... arg types here ...] return type
> here]]))
> 
> (defn -main [args*] (...do smth...))
> (defn pre-method_name1 [args*] (...do smth...))
> (defn pre-method_name2 [args*] (...do smth...))
> 
> In example: method_name1 is a method because it is included in gen-
> class clause, -method_name2 is clojure function.

In fact both are clojure functions. However you can call (.method_name1 obj) 
but not (.method_name2 obj).

> But what about main?
> Is it a function(not method) because prefix was changed or not?

main is special. You can tell whether to generate a static main method via 
":main true" or ":main false" in the :gen-class clause. true is the default. So 
in you example a main method will be generated, but it can't be used, because 
there is no function called pre-main. -main is a normal clojure function (as 
would be pre-main if it was defined).

> And what function's names can be used to declare class method without
> including them to gen-class clause? (main and what else?)

Only main is of that sort. And methods from interfaces and super classes don't 
have to be declared. In fact they are not allowed to be declared.

Sincerely
Meikel

-- 
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your 
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en

Re: clojure gen-class questions

[Meikel Brandmeyer]

Hi,

I wrote up a post: http://tr.im/NwCL

Hope it helps.

Sincerely
Meikel

-- 
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your 
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en

Re: Trait-like behavior with Protocols

[aria42]

If this situation is common enough, shouldn't defprotocol support
optional implementations which are implicitly merged?

On Feb 9, 6:01 am, Konrad Hinsen  wrote:
> On 09.02.2010, at 02:14, Stuart Sierra wrote:
>
> > On Feb 8, 6:13 pm, aria42  wrote:
> >> (defprotocol Span
> >>   (start [self])
> >>   (stop [self])
> >>   (span-length [self]))
>
> >> Now I know I can just make span-length a function on Span as opposed
> >> to part of the protocol. Is that what one should do?
>
> > Yes.
>
> I would say "it depends".
>
> I have a similar situation in my multiarray package 
> (http://code.google.com/p/clj-multiarray/). In the multiarray protocol, I 
> have two functions, "shape" and "rank", with the latter being by definition 
> the same as (comp count shape). However, I still have "rank" in the protocol, 
> because for some implementations it is more efficient to compute the rank 
> directly, rather than construct a shape vector just for computing its length 
> afterwards.
>
> In such situations it is useful to provide a default implementation and leave 
> it up to each type to implement a more efficient alternative or not. With 
> extend and the maps that go with it, this is easy to achieve: make a map with 
> the default implementations, and merge this with the type-specific 
> implementations fed to extend.
>
> Konrad.

-- 
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your 
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en

Re: Prepping clojure for packaging (was: Re: Clojure for system administration)

[Peter Schuller]

> That's exactly what Debian does. For every Java package also provide
> the maven xml file and the jar is discoverable from maven. The
> installed packages on the local system acts as a local maven repo.
>
>  

I see they also solved the problem of not downloading during build.

One should probably look into doing something similar for other
packaging systems then.

Guess I need to bite the bullet and learn Maven ;)

-- 
/ Peter Schuller

-- 
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your 
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en

Re: Detecting Number of Available CPU Threads

[Chouser]

On Mon, Feb 8, 2010 at 8:37 PM, Wardrop  wrote:
> That seems like what I'm after, thanks. I assume this would be pretty
> reliable across all platforms running the JVM.
>
> By the way, I did google the Java API with various keywords but never
> cam across this object property.

It may be worth noting that using 'send' to dispatch actions to
an agent already takes into account the number of CPUs available.
This essentially means it's safe to queue up sends on as many
agents as you want -- hundreds, even thousands of agents --
regardless of how many CPUs are on your current host.

The same is *not* true of 'send-off' or 'future', which do not
have bounds on their thread pool.

--Chouser
http://joyofclojure.com/

-- 
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your 
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en

Re: clojure gen-class questions

[Brian Wolf]

Hi,

I also am confused about gen-class, looking for a pointer to some code 
examples.


Thanks,

Brian

???  wrote:

Oh...So to make methods I must declare them in gen-class clause and if
some function wasn't include in gen-class clause, it wouldn't be a
method even if it had a prefix from gen-class clause.
I mean:
(ns example.class
  (:gen-class
   :prefix pre-
   :methods [[method_name1 [... arg types here ...] return type
here]]))

(defn -main [args*] (...do smth...))
(defn pre-method_name1 [args*] (...do smth...))
(defn pre-method_name2 [args*] (...do smth...))

In example: method_name1 is a method because it is included in gen-
class clause, -method_name2 is clojure function. But what about main?
Is it a function(not method) because prefix was changed or not?

And what function's names can be used to declare class method without
including them to gen-class clause? (main and what else?)

  


--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your 
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en

Re: clojure gen-class questions

[Аркадий Рост]

And one more, when and why "methods" should be used? (except main)

-- 
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your 
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en

Re: clojure gen-class questions

[Аркадий Рост]

Oh...So to make methods I must declare them in gen-class clause and if
some function wasn't include in gen-class clause, it wouldn't be a
method even if it had a prefix from gen-class clause.
I mean:
(ns example.class
  (:gen-class
   :prefix pre-
   :methods [[method_name1 [... arg types here ...] return type
here]]))

(defn -main [args*] (...do smth...))
(defn pre-method_name1 [args*] (...do smth...))
(defn pre-method_name2 [args*] (...do smth...))

In example: method_name1 is a method because it is included in gen-
class clause, -method_name2 is clojure function. But what about main?
Is it a function(not method) because prefix was changed or not?

And what function's names can be used to declare class method without
including them to gen-class clause? (main and what else?)

-- 
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your 
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en

Re: clojure gen-class questions

[Аркадий Рост]

Thaks for yor answer. It's really help me with studying.

-- 
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your 
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en

Re: clojure gen-class questions

[Meikel Brandmeyer]

Hi,

On Feb 9, 4:22 pm, Аркадий Рост  wrote:

> For example:
>
> (ns exaple_class
>     (:gen-class))
>
> (defn -main [args*] (...do smth...))
> (defn -method_name1 [args*] (...do smth...))
> (defn- -method_name2 [args*] (...do smth...))
> (def -a 5)
>
> (defn fun1 [args*] (...do smth...))
> (defn- fun2 [args*] (...do smth...))
> (def b 5)
>
> As I understand, in this example we'll get java class. It's name test
> and it contains methods: main, method_name1, method_name2.

No. It just has a static method main (which is specially treated). To
make method_name1 and method_name2 you must declare so in the gen-
class clause.

(ns example.class
  (:gen-class
:methods [[method_name1 [... arg types here ...] return type here]
  [method_name1 [... arg types here ...] return type here]
  #^{:static true} [some_static_method ]]))

> What does it mean that method_name2 is declared as private?

The "methods" are just plain old clojure function. The real methods
are stubs which call these functions. So you can basically call the
method functions directly. If method_name2 is private this can only be
done from the same namespace. For (.method_name2 obj ...) form of
calling the private flag is not of interest and works from everywhere.

> Then what classes will contain functions fun1, fun2?

No class will contain those functions, because they are not declared
in the :gen-class clause.

> fun2 defined with defn- so it will be private, but for what does it
> mean?

See above for method_name2.

> Also is there difference beetwen declaration -a and b?

It's just a different name. Otherwise they will behave the same.

> what classes are they containing in?

No classes will contain -a or b. gen-class'd classes cannot contain
"fields". You can only specify a state (via :state in the :gen-class
clause). However the state can be a map, which can hold different
other values. However it is immutable. So if you want to modify the
state you have to wrap into a ref or atom.

See also: http://clojure.org/compilation

Hope this helps.

Sincerely
Meikel

-- 
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your 
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en

clojure gen-class questions

[Аркадий Рост]

Hi!
For example:

(ns exaple_class
(:gen-class))

(defn -main [args*] (...do smth...))
(defn -method_name1 [args*] (...do smth...))
(defn- -method_name2 [args*] (...do smth...))
(def -a 5)

(defn fun1 [args*] (...do smth...))
(defn- fun2 [args*] (...do smth...))
(def b 5)

As I understand, in this example we'll get java class. It's name test
and it contains methods: main, method_name1, method_name2.
What does it mean that method_name2 is declared as private?

Then what classes will contain functions fun1, fun2?
fun2 defined with defn- so it will be private, but for what does it
mean?

Also is there difference beetwen declaration -a and b? what classes
are they containing in?



-- 
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your 
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en

Re: Trait-like behavior with Protocols

[Konrad Hinsen]

On 09.02.2010, at 02:14, Stuart Sierra wrote:

> On Feb 8, 6:13 pm, aria42  wrote:
>> (defprotocol Span
>>   (start [self])
>>   (stop [self])
>>   (span-length [self]))
>> 
>> Now I know I can just make span-length a function on Span as opposed
>> to part of the protocol. Is that what one should do?
> 
> Yes.

I would say "it depends".

I have a similar situation in my multiarray package 
(http://code.google.com/p/clj-multiarray/). In the multiarray protocol, I have 
two functions, "shape" and "rank", with the latter being by definition the same 
as (comp count shape). However, I still have "rank" in the protocol, because 
for some implementations it is more efficient to compute the rank directly, 
rather than construct a shape vector just for computing its length afterwards.

In such situations it is useful to provide a default implementation and leave 
it up to each type to implement a more efficient alternative or not. With 
extend and the maps that go with it, this is easy to achieve: make a map with 
the default implementations, and merge this with the type-specific 
implementations fed to extend.

Konrad.

-- 
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your 
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en

Re: error reporting for macro expansion

[Jeff Rose]

I agree, the error reporting from the compiler can often be hard to
dig through.  Besides showing both the location of the macro
definition and its usage, it would be nice to hide all of the
clojure.lang.* calls in the stack trace by default, or fold them into
a single line.  That way the user code in the callstack would be
separated by 1 line rather 10 or 20, so you could more easily trace
the execution path.

On Feb 8, 8:11 pm, "John R. Williams"  wrote:
> The Clojure compiler is not very helpful when it comes to debugging
> exceptions that occur while macros are being expanded. As an example,
> consider this code:
>
> ;; macro-fail.clj
> (defmacro broken [] (/ 0 0))
> (broken)
>
> Here's the stack trace I get when I compile this file:
>
> Exception in thread "main" java.lang.ArithmeticException: Divide by
> zero (macro-fail.clj:0)
>         at clojure.lang.Compiler.eval(Compiler.java:5365)
>         at clojure.lang.Compiler.load(Compiler.java:5759)
>         at clojure.lang.Compiler.loadFile(Compiler.java:5722)
>         at clojure.main$load_script__5893.invoke(main.clj:213)
>         at clojure.main$script_opt__5922.invoke(main.clj:265)
>         at clojure.main$main__5940.doInvoke(main.clj:346)
>         at clojure.lang.RestFn.invoke(RestFn.java:409)
>         at clojure.lang.Var.invoke(Var.java:365)
>         at clojure.lang.AFn.applyToHelper(AFn.java:165)
>         at clojure.lang.Var.applyTo(Var.java:482)
>         at clojure.main.main(main.java:37)
> Caused by: java.lang.ArithmeticException: Divide by zero
>         at clojure.lang.Numbers.divide(Numbers.java:138)
>         at user$broken__1.invoke(macro-fail.clj:2)
>         at clojure.lang.Var.invoke(Var.java:369)
>         at clojure.lang.AFn.applyToHelper(AFn.java:167)
>         at clojure.lang.Var.applyTo(Var.java:482)
>         at clojure.lang.Compiler.macroexpand1(Compiler.java:5212)
>         at clojure.lang.Compiler.macroexpand(Compiler.java:5267)
>         at clojure.lang.Compiler.eval(Compiler.java:5335)
>         ... 10 more
>
> As you can see, line 3, where the macro is used, appears nowhere in
> the stack trace. I've made some progress addressing this issue by
> adding an exception handler in Compiler.macroexpand1. I also
> discovered that, although the reader attaches line numbers to the
> forms it reads, it does not attach file names. I've added some code in
> LispReader.java that attaches the file name, but it does so by getting
> the value of Compiler.SOURCE_PATH. I suspect a less hackish fix would
> involve passing a filename to the reader some other way.

-- 
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your 
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en

Re: scope of binding

[Alex]

D'oh! Thanks.

I fall for that trap yet again. Sounds so simple when explained.

2010/2/9 Sean Devlin :
> The problem is that map returns a lazy seq, and the lazy seq is
> evaluated outside of the binding by the REPL.  If you add a doall
> inside the binding, it behaves as you expect.
>
> user=> (binding [*v* 2] (doall (map f [1 1 1])))
> (3 3 3)
>
> Sean

I know I've omitted this detail, but the actual code in question is
actually *db* binding from clojure.contrib.sql, so I can't change it
either way. doall works fine though.

2010/2/9 Richard Newman :
> You can also capture the binding. This looks a little ugly, but it works: it
> grabs the binding eagerly, and returns a closure that dynamically binds it
> when the function is invoked.
>
> (binding [*v* 2]
>  (map (let [v *v*]
>         (fn [n]
>           (binding [*v* v]
>             (f n
>       [1 1 1]))
>
> Obviously you wouldn't use it in this instance -- use doall, or better yet
> rewrite your function to not use dynamic bindings -- but for larger jobs it
> works fine.

-- 
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your 
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en

Re: Prepping clojure for packaging (was: Re: Clojure for system administration)

[Ramakrishnan Muthukrishnan]

On Tue, Feb 9, 2010 at 12:27 PM, Meikel Brandmeyer  wrote:
> Hi,
>
> maybe I don't understand the problem. Why can't the system provide
> some kind of local repository? The package system (deb, rpm, ports,
> whatever) just installs the dependencies there. A wrapper script reads
> in the dependencies and adds them to the classpath on program start.
> Nothing is downloaded. There might be several versions of a library
> installed. No global classpath. I think that's what maven/ivy do right
> now. Why wouldn't this work together with a packaging system? (I think
> FreeBSD shows the way to go: cooperation between the system and the
> language.)

That's exactly what Debian does. For every Java package also provide
the maven xml file and the jar is discoverable from maven. The
installed packages on the local system acts as a local maven repo.

 

-- 
  Ramakrishnan

-- 
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your 
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en

Re: Please share your thoughts on dependency injection

[Steve Purcell]

On 8 Feb 2010, at 16:53, Boris Mizhen - 迷阵 wrote:

> Hello all,
> 
> I am playing with the idea of a little library for dependency injection.
> The idea is to declare injectable values as metadata-to-function map.
> I started with a sketch of what the client code may look like.
> 
> Please let me know what you think.


I think you could achieve the same effect much more simply using 
'binding'/'with-bindings' and 'memoize'.

-Steve

-- 
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your 
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en

Re: Trait-like behavior with Protocols

[Jeff Rose]

I think the extend function is made exactly to support the concrete
implementation of protocols.  It takes a type, and then any number of
protocol + function map pairs, where keyword names map to functions.
Checkout the protocol docs on assembla and look for extend:

http://www.assembla.com/wiki/show/clojure/Protocols

or read a recent post by Rich where he talks about some of the design
decisions behind these constructs:

http://groups.google.com/group/clojure/msg/330c230e8dc857a9

-Jeff Rose

On Feb 9, 12:13 am, aria42  wrote:
> Is it possible to have default implementations associated with
> functions in a protocol? This is most useful when some protocol
> functions are defined in terms of other. For instance,
>
> (defprotocol Span
>   (start [self])
>   (stop [self])
>   (span-length [self]))
>
> Now I know I can just make span-length a function on Span as opposed
> to part of the protocol. Is that what one should do?

-- 
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your 
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en