eval-when-load?

eval-when-load?

[Stephen Leake]

A project I'm working on has a form like this at top level in a file:

(defvar jde-jdhelper-singleton (jde-jdhelper nil)
  "The JDHelper singleton instance.")

`jde-jdhelper' can throw an error, which it does during byte-compile (it
complains about not finding "wget").

We want the variable defined at load time, and we want the error at load
time, but we don't care at compile time.

So I'd like to do:

(eval-when-load
 (defvar jde-jdhelper-singleton (jde-jdhelper nil)
   "The JDHelper singleton instance."))

but `eval-when-load' is not defined.

Is there a work-around?

We could change the var to a function that checks if the initialization
is done, but that seems a heavy solution. 

-- 
-- Stephe

Re: eval-when-load?

[Artur Malabarba]

Is jde-jdhelper a macro? If it's a function the behavior you're asking
about is the default.

For instance, if I add (defvar oi (mapcar 'car nil)) to a file and
compile it, the byte-compiled file will be identical.

2015-07-16 17:33 GMT+01:00 Stephen Leake <stephen_leake@stephe-leake.org>:
> A project I'm working on has a form like this at top level in a file:
>
> (defvar jde-jdhelper-singleton (jde-jdhelper nil)
>   "The JDHelper singleton instance.")
>
> `jde-jdhelper' can throw an error, which it does during byte-compile (it
> complains about not finding "wget").
>
> We want the variable defined at load time, and we want the error at load
> time, but we don't care at compile time.
>
> So I'd like to do:
>
> (eval-when-load
>  (defvar jde-jdhelper-singleton (jde-jdhelper nil)
>    "The JDHelper singleton instance."))
>
> but `eval-when-load' is not defined.
>
> Is there a work-around?
>
> We could change the var to a function that checks if the initialization
> is done, but that seems a heavy solution.
>
> --
> -- Stephe
>

Re: eval-when-load?

[Stephen Leake]

Artur Malabarba <bruce.connor.am@gmail.com> writes:

> Is jde-jdhelper a macro? If it's a function the behavior you're asking
> about is the default.

jde-jdehelper is an eieio class:

(require 'eieio)

(defclass jde-jdhelper ()
 ...)
 

-- 
-- Stephe

Re: eval-when-load?

[Philipp Stephani]

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Stephen Leake <stephen_leake@stephe-leake.org> schrieb am Do., 16. Juli
2015 um 18:34 Uhr:

> So I'd like to do:
>
> (eval-when-load
>  (defvar jde-jdhelper-singleton (jde-jdhelper nil)
>    "The JDHelper singleton instance."))
>
> but `eval-when-load' is not defined.
>

cl-lib has (cl-eval-when (load) ...)

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Re: eval-when-load?

[Stefan Monnier]

> A project I'm working on has a form like this at top level in a file:
> (defvar jde-jdhelper-singleton (jde-jdhelper nil)
>   "The JDHelper singleton instance.")
> `jde-jdhelper' can throw an error, which it does during byte-compile (it
> complains about not finding "wget").
> We want the variable defined at load time, and we want the error at load
> time, but we don't care at compile time.

I suspect there's a confusion about "compile time": the above call to
jde-jdhelper will not be executed while compiling the file that contains
this defvar.  It will only be called when the resulting .elc file is
loaded (so, as Artur says, what you ask is already the default
behavior).

But I suspect the problem you see is that the above form appears in
a file which is not only byte-compiled but is also `require'd by other
files in that package, so when *those* files are byte-compiled, the call
to jde-jdhelper is indeed executed, since at that time this file is
loaded (as part of byte-compiling those other files).

Maybe you want to use

   (if t (require 'this-file))

instead of (require 'this-file) so that this-file is only loaded when
those-files are *loaded* rather than when they're byte-compiled.

Of course, the same problem can happen if those-files are themselves
`require'd by yet-other-files, in which case they may end up being
loaded during compilation of those-yet-other-files, at which point
they'll also load this-file.  In that case, you want like to again
replace (require 'that-file) with (if t (require 'that-file)) to avoid
loading those-files during byte-compilation of those-yet-other-files.


        Stefan

Re: eval-when-load?

[Stephen Leake]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

> But I suspect the problem you see is that the above form appears in
> a file which is not only byte-compiled but is also `require'd by other
> files in that package, so when *those* files are byte-compiled, the call
> to jde-jdhelper is indeed executed, since at that time this file is
> loaded (as part of byte-compiling those other files).

Yes, that's it.

> Maybe you want to use
>
>    (if t (require 'this-file))
>
> instead of (require 'this-file) so that this-file is only loaded when
> those-files are *loaded* rather than when they're byte-compiled.

This almost works; I still get errors, because jde-jdhelper is a macro,
and the variable itself is referenced, so I need this-file loaded at
compile-time. Sigh.

-- 
-- Stephe

Re: eval-when-load?

[Stefan Monnier]

> This almost works; I still get errors, because jde-jdhelper is a macro,
> and the variable itself is referenced, so I need this-file loaded at
> compile-time. Sigh.

I'm not surprised.  It's usually easier&better to arrange for the
initialization code that signals the error to only run when the code is
really activated, rather than when the files are loaded.


        Stefan