access of global variables from modules

access of global variables from modules

[Mr. Peter Ivanyi]

Hello again,

I have another problem with modules.
If I have a module can the module access "global" variables.
I have an application, which defines some global variables. 
The application also loads some modules and I would like to access
the global variables from the module. 
How can I do it ? (I think I can put the global variables into a module
and another module can depend on it, but isn't there another way ?)

For example I have this module (gen.scm):
----------------------
(define-module (gen gen))
(export gen-hello)

(define (gen-hello)
  (set! *G* 3)
  (display "Hello World !")
  (newline)
)
-------------------------

then I receive this

-------------------------
peteri@mercury $ guile
guile> (define *G* 1)
guile> (use-modules (gen gen))
guile> (gen-hello)
./gen/gen.scm:7:1: In expression (set! *G* 3):
./gen/gen.scm:7:1: Unbound variable: *G*
ABORT: (unbound-variable)

Type "(backtrace)" to get more information or "(debug)" to enter the debugger.
guile> 
-------------------------

instead of setting *G* to 3 and then print "Hello World !".

Thanks, for your help in advance.

					Peter Ivanyi

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Re: access of global variables from modules

[Neil Jerram]

>>>>> "Peter" == Peter Ivanyi <peteri@carme.sect.mce.hw.ac.uk> writes:

    Peter> Hello again,
    Peter> I have another problem with modules.
    Peter> If I have a module can the module access "global" variables.
    Peter> I have an application, which defines some global variables. 
    Peter> The application also loads some modules and I would like to access
    Peter> the global variables from the module. 
    Peter> How can I do it ? (I think I can put the global variables into a module
    Peter> and another module can depend on it, but isn't there another way ?)

    Peter> For example I have this module (gen.scm):
    Peter> ----------------------
    Peter> (define-module (gen gen))
    Peter> (export gen-hello)

    Peter> (define (gen-hello)
    Peter>   (set! *G* 3)
    Peter>   (display "Hello World !")
    Peter>   (newline)
    Peter> )
    Peter> -------------------------

What exactly do you mean by a global variable?  Every variable must be
defined in some module, and in this case what you need to do is:

- export *G* from the module in which it is defined

- in (gen gen), `use' that module.

If you say that *G* is global, you probably mean that it is defined in
the (guile-user) module.  So what you need is:

;; ... just after the definition of *G* ...
(export *G*)

;; In gen.scm after the define-module line ...
(use-modules (guile-user))

Please let me know if this helps.

        Neil


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Re: access of global variables from modules

[Mr. Peter Ivanyi]

> What exactly do you mean by a global variable?  Every variable must be
> defined in some module, and in this case what you need to do is:
[...]
> Please let me know if this helps.
> 

Aha, now I think I am beginning to get the idea. Yes this definitely 
helps. What was confusing for me (and I did not find it in the 
documentation which I have) that when I start guile I am already in the 
"guile-user" or the "guile" module. That is why I thought there is some 
kind of "global" environement and all modules are defined in this 
"global" environment.

Thanks again,

					Peter Ivanyi

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Re: access of global variables from modules

[Neil Jerram]

>>>>> "Peter" == Peter Ivanyi <peteri@carme.sect.mce.hw.ac.uk> writes:

    >> What exactly do you mean by a global variable?  Every variable must be
    >> defined in some module, and in this case what you need to do is:
    Peter> [...]
    >> Please let me know if this helps.
    >> 

    Peter> Aha, now I think I am beginning to get the idea. Yes this definitely 
    Peter> helps. What was confusing for me (and I did not find it in the 
    Peter> documentation which I have) that when I start guile I am already in the 
    Peter> "guile-user" or the "guile" module. That is why I thought there is some 
    Peter> kind of "global" environement and all modules are defined in this 
    Peter> "global" environment.

Great; I hope to be working on the documentation for modules soon, and
I'll make sure to include this point.

        Neil


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