new, macros and "Can't eval locals"

[AtKaaZ]

The goal is to can write this form:
=> (let [a java.lang.RuntimeException]
     (new a)
     )
CompilerException java.lang.IllegalArgumentException: Unable to resolve classname: a, compiling:(NO_SOURCE_PATH:2:3)

attempt with macro:

=> (defmacro mew [cls & restt]
     `(new ~(eval cls) ~@restt)
     )
#'runtime.q/mew
=> (let [a java.lang.RuntimeException]
     (mew a)
     )
CompilerException java.lang.UnsupportedOperationException: Can't eval locals, compiling:(NO_SOURCE_PATH:2:3)

attempt with function:
=> (defn mew [cls & restt]
     (new cls)
     )
CompilerException java.lang.IllegalArgumentException: Unable to resolve classname: cls, compiling:(NO_SOURCE_PATH:2:3)

attempt with a macro inside the function:
=> (defn mew [cls & restt]
     (mew cls)
     )
CompilerException java.lang.UnsupportedOperationException: Can't eval locals, compiling:(NO_SOURCE_PATH:2:3)

Ok, i give up, how? impossible ?

--

Please correct me if I'm wrong or incomplete,
even if you think I'll subconsciously hate it.

[Andy Fingerhut]

On Feb 14, 2013, at 1:27 PM, AtKaaZ wrote:

The goal is to can write this form:
=> (let [a java.lang.RuntimeException]
     (new a)
     )
CompilerException java.lang.IllegalArgumentException: Unable to resolve classname: a, compiling:(NO_SOURCE_PATH:2:3)

attempt with macro:

=> (defmacro mew [cls & restt]
     `(new ~(eval cls) ~@restt)
     )
#'runtime.q/mew

This is probably your closest attempt.  Try this variation on the above:

(defmacro mew [cls & args]

  `(new ~cls ~@args))

user=> (macroexpand-1 '(mew java.lang.RuntimeException))

(new java.lang.RuntimeException)

Andy

[AtKaaZ]

thanks for the reply,

=> (defmacro mew [cls & args]
     `(new ~cls ~@args))
#'runtime.q/mew
=> (let [a java.lang.RuntimeException]
     (mew a)
     )

CompilerException java.lang.IllegalArgumentException: Unable to resolve classname: a, compiling:(NO_SOURCE_PATH:2:3)

that would be the equivalent macro of what new is doing

it's like
(new a)

CompilerException java.lang.IllegalArgumentException: Unable to resolve classname: a, compiling:(NO_SOURCE_PATH:2:3)

This is the goal:

The goal is to can write this form:
=>  (let [a java.lang.RuntimeException]
         (new a))

but I think it's impossible, at least by using "new" it is

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[AtKaaZ]

I figure since new is expecting a class at compiletime, we can never pass it a class that we evaluate at runtime(those locals), ergo => impossible to macro around "new" like that

like this => impossible:
(let [a java.lang.RuntimeException]
         (macro-that-eventually-calls-new a))

maybe someone could suggest another way? clojure.reflect ?

[AtKaaZ]

ok looks like it's not impossible:
=> (defmacro mew [cls & restt]
     (let [c a]
       `(eval (new ~a ~@restt))
       )
     )

#'runtime.q/mew
=> (let [a java.lang.RuntimeException]
     (mew a)
     )

#<RuntimeException java.lang.RuntimeException>

[AtKaaZ]

ah I tricked myself... I used "~a"  inside the macro instead of "~c" or "~cls"

so back to still impossible

=> (defmacro mew [cls & restt]

     (let [c cls]
       `(eval (new ~c ~@restt))

       )
     )
#'runtime.q/mew
=> (let [a java.lang.RuntimeException]
     (mew a)
     )

CompilerException java.lang.IllegalArgumentException: Unable to resolve classname: a, compiling:(NO_SOURCE_PATH:2:3)

=> (defmacro mew [cls & restt]

     `(eval (new ~cls ~@restt))

     )
#'runtime.q/mew
=> (let [a java.lang.RuntimeException]
     (mew a)
     )

CompilerException java.lang.IllegalArgumentException: Unable to resolve classname: a, compiling:(NO_SOURCE_PATH:2:3)

[AtKaaZ]

and I forgot to mention that I already had another "a" defined
=> a
java.lang.RuntimeException

hence why it worked

[Aaron Cohen]

Yes, since this is runtime you should use reflection.

(let [a java.lang.RuntimeException]

   (.newInstance a))

Alternatively, you can use eval:

(let [a java.lang.RuntimeException]

  (eval (list 'new a)))

[AtKaaZ]

Thank you! I didn't know you could do .newInstance

oh that's a nice trick with eval and list 'new

So it's not impossible after all, thanks Aaron!

Here's what I got from what you said:
=>

(defmacro mew [cls & restt]
       `(eval (list 'new ~cls ~@restt))
     )

#'runtime.q/mew
=> (let [a java.lang.RuntimeException]
       (mew a)
     )

#<RuntimeException java.lang.RuntimeException>

it makes sense now, using eval at runtime not at compile time as I was trying

and also the newInstance variant:
=> (defmacro mew [cls & restt]
       `(.newInstance ~cls ~@restt)
     )

#'runtime.q/mew
=> (let [a java.lang.RuntimeException]
       (mew a)
     )

#<RuntimeException java.lang.RuntimeException>

Really, thank you Aaron,

[Jacob Goodson]

You need to know something... it's a dialect of LISP, the only limitation is you.

[AtKaaZ]

On Sun, Feb 17, 2013 at 6:12 AM, Jacob Goodson <submissio...@gmx.com> wrote:

You need to know something... it's a dialect of LISP, the only limitation is you.

though it is certainly exerting its limitations on me