Re : [Chicken-users] do I use define-foreign-variable correctly ?

[minh thu]

2007/2/7, Kon Lovett <address@hidden>:
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> On Feb 7, 2007, at 6:41 AM, minh thu wrote:
>
> > #>!
> > #include <X.h>
> > #include <keysym.h>
> > <#
> >
> > (define-foreign-variable c-escape-key int "XK_Escape")
> > (define escape-key c-escape-key)
> >
> > Do I need to have those two lines too be able to use escape-key as a
> > Scheme symbol for the C #defined XK_Escape value ?
>
> Umm, depends. Do you want it visible outside of the compilation unit
> (i.e. exportable)?

The escape-key, yes; the c-escape-key, no.

> then '(define escape-key (foreign-value
> "XK_Escape" int))' is enough.

Thanks !

> (I might make the symbol uppercase just
> to emphasize it is a constant.)

Ok.

> Also 'define-foreign-variable' has
> overhead that you don't want for a constant, it isn't mutable so
> conversion should only be done once. ('foreign-value' is a wrapper
> around 'define-foreign-variable' that creates the variable, gets its'
> value, & throws away the variable, returning only the value.)

Do I understand correctly : define-foreign-variable has overhead in this
case since I don't need it to be mutable and foreign-value has not
that overhead ?

Thanks,
thu