Re: Dynamically creating defrecord

[JUAN ANTONIO Ruz]

Hi Sven, 
I was trying to do the same with my library tangrammer/defrecord-wrapper 
 and, just today, I found 
a couple of links that worked fine for that
http://grokbase.com/t/gg/clojure/11cjvz1jda/defrecord-based-on-runtime-metadata
http://stackoverflow.com/questions/3748559/clojure-creating-new-instance-from-string-class-name

I integrated the solution here making a lazy-seq of dynamic defrecords
https://github.com/milesian/aop/blob/master/src/milesian/aop.clj#L20


hope it helps
Juan



El sábado, 17 de enero de 2015, 17:27:05 (UTC), Sven Richter escribió:
>
> Hi,
>
> I am trying to create record definitions dynamically during runtime. What 
> I would like to do is something like this:
>
> (defn mk-rec [record-name namespace arg-list]
>   (eval '(do (ns namespace)
>(defrecord record-name arg-list
>
> And then call it like this:
> (mk-rec "A" "ns" [a b c])
> (->ns.A 1 2 3 )
>
> I am trying out different things, but struggle to get it right or find 
> some tutorial for it.
>
> So if anyone is willing to share some working code I'd be really happy.
>
> Thanks,
> Sven
>

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Re: Dynamically creating defrecord

[Sven Richter]

Thank you all for your answers and insights. As it often turns out, I don't 
need them. Clara rules also exposes other ways to pass data into rules.

Best Regards,
Sven

On Sunday, January 18, 2015 at 3:34:17 AM UTC+1, Sean Corfield wrote:
>
> On Jan 17, 2015, at 3:04 PM, Matching Socks  > wrote: 
> > And defstruct has not been deprecated in the API documentation. 
>
> Technically true but when you see comments like these out there it’s 
> reasonable to assume that structs should be avoided: 
>
> "We intentionally omit ... struct-maps, which are deprecated" 
> -- Prismatic Engineering Practices 
> -- 
> https://github.com/Prismatic/eng-practices/blob/master/clojure/20130926-data-representation.md#data-types
>  
>
> "I consider structs to be effectively deprecated so I don't use them at 
> all." 
> -- Alex Miller 
> -- 
> http://stackoverflow.com/questions/4575170/where-should-i-use-defrecord-in-clojure/4576143#4576143
>  
>
> "Incidentally, unless you need to stick to Clojure 1.1, you might want to 
> use 1.2's defrecord in preference to defstruct -- in fact, the latter is 
> deprecated in 1.2." 
> -- Michał Marczyk 
> -- 
> http://stackoverflow.com/questions/4288360/clojures-macro-define-a-binding-whose-name-is-composed-from-an-argument/4288738#4288738
>  
>
> Sean Corfield -- (904) 302-SEAN 
> An Architect's View -- http://corfield.org/ 
>
> "Perfection is the enemy of the good." 
> -- Gustave Flaubert, French realist novelist (1821-1880) 
>
>
>
>

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Re: Dynamically creating defrecord

[Sean Corfield]

On Jan 17, 2015, at 3:04 PM, Matching Socks  wrote:
> And defstruct has not been deprecated in the API documentation.

Technically true but when you see comments like these out there it’s reasonable 
to assume that structs should be avoided:

"We intentionally omit ... struct-maps, which are deprecated"
-- Prismatic Engineering Practices
-- 
https://github.com/Prismatic/eng-practices/blob/master/clojure/20130926-data-representation.md#data-types

"I consider structs to be effectively deprecated so I don't use them at all."
-- Alex Miller
-- 
http://stackoverflow.com/questions/4575170/where-should-i-use-defrecord-in-clojure/4576143#4576143

"Incidentally, unless you need to stick to Clojure 1.1, you might want to use 
1.2's defrecord in preference to defstruct -- in fact, the latter is deprecated 
in 1.2."
-- Michał Marczyk
-- 
http://stackoverflow.com/questions/4288360/clojures-macro-define-a-binding-whose-name-is-composed-from-an-argument/4288738#4288738

Sean Corfield -- (904) 302-SEAN
An Architect's View -- http://corfield.org/

"Perfection is the enemy of the good."
-- Gustave Flaubert, French realist novelist (1821-1880)



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Re: Dynamically creating defrecord

[Lee Spector]

> On Jan 17, 2015, at 6:04 PM, Matching Socks  wrote:
> 
> Did you find something really wrong with defstruct?  Occasions when the basis 
> fields are not known to the programmer seem better met by defstruct than 
> defrecord.  And defstruct has not been deprecated in the API documentation.  
> The comment "Note: Most uses of StructMaps would now be better served by 
> records"[1] probably refers to times when you know the fields!  Is there 
> really a need to bend over backwards to switch natural defstruct usage over 
> to records?
> 
> [1] http://clojure.org/data_structures 

I had thought that there was something closer to deprecation of defstruct in 
the documentation, or at least that deprecation was advocated by lots of people 
when we discussed it there.

And then we did some speed tests in our application, and at least from the 
tests that we did, it appeared records were indeed faster by an amount that 
mattered for us.

 -Lee

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Re: Dynamically creating defrecord

[Christopher Small]

The reason you can't just call `(mk-rec "A" "ns" [a b c])` is that your 
`mk-rec` is a function, and `a`, `b`, and `c` are undefined. To have them 
interpretted as symbols, you'd either have to explicitly use `['a 'b 'c]`, 
or write `mk-rec` as a macro (as Lee points towards).

I was able to get a macro that does _almost_ what you want, but wasn't 
quite able to get the namespacing right (at least cleanly). If you need 
some reading on macros, I really enjoyed the Joy of Clojure's presentation. 
The [Clojure for the Brave and True 
treatment](http://www.braveclojure.com/writing-macros/) seems good, but 
glimpsing through I found there were a couple of little idioms/tricks that 
were missing that would have been nice to see. Still a good place to start 
though probably.

Chris

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Re: Dynamically creating defrecord

[James Reeves]

On 17 January 2015 at 17:27, Sven Richter  wrote:
>
> I am trying to create record definitions dynamically during runtime.
>

To what end? The right answer depends very much on your end goal.

- James

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Re: Dynamically creating defrecord

[Matching Socks]

Did you find something really wrong with defstruct?  Occasions when the 
basis fields are not known to the programmer seem better met by defstruct 
than defrecord.  And defstruct has *not* been deprecated in the API 
documentation.  The comment "Note: Most uses of StructMaps would now be 
better served by records"[1] probably refers to times when you know the 
fields!  Is there really a need to bend over backwards to switch natural 
defstruct usage over to records?

[1] http://clojure.org/data_structures

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Re: Dynamically creating defrecord

[Lee Spector]

> On Jan 17, 2015, at 12:27 PM, Sven Richter  wrote:
> 
> I am trying to create record definitions dynamically during runtime. What I 
> would like to do is something like this:
> 
> (defn mk-rec [record-name namespace arg-list]
>   (eval '(do (ns namespace)
>(defrecord record-name arg-list
> 
> And then call it like this:
> (mk-rec "A" "ns" [a b c])
> (->ns.A 1 2 3 )
> 
> I am trying out different things, but struggle to get it right or find some 
> tutorial for it.
> 
> So if anyone is willing to share some working code I'd be really happy.

In case it may help I'll paste in below some related code from my Clojush 
project (https://github.com/lspector/Clojush 
).

The stuff commented out at the top is how I used to do it with defstruct, which 
I preferred, but that was a very unpopular perspective. The stuff below is how 
we do it now with defrecord.

 Best, 

 -Lee

;(defmacro define-push-state-structure []
;  `(defstruct push-state ~@push-types))

;(define-push-state-structure)

;(defn make-push-state
;  "Returns an empty push state."
;  []
;  (struct-map push-state))

;; record-based states (apparently faster)

(defn keyword->symbol [kwd]
 "Returns the symbol obtained by removing the : from a keyword."
 (symbol (name kwd)))

(defmacro define-push-state-record-type []
 `(defrecord ~'PushState [~@(map keyword->symbol push-types)]))

(define-push-state-record-type)

(let [empty-state (map->PushState {})]
  (defn make-push-state
"Returns an empty push state."
[] empty-state))

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Dynamically creating defrecord

[Sven Richter]

Hi,

I am trying to create record definitions dynamically during runtime. What I 
would like to do is something like this:

(defn mk-rec [record-name namespace arg-list]
  (eval '(do (ns namespace)
   (defrecord record-name arg-list

And then call it like this:
(mk-rec "A" "ns" [a b c])
(->ns.A 1 2 3 )

I am trying out different things, but struggle to get it right or find some 
tutorial for it.

So if anyone is willing to share some working code I'd be really happy.

Thanks,
Sven

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