Re: Bug?? [defined? and modules]

[Marius Vollmer <mvo@zagadka.ping.de>]

Chris Bitmead <chrisb@ans.com.au> writes:

> Does the following behaviour indicate a bug??
> 
> guile> dynamic-link
> #<primitive-procedure dynamic-link>
> guile> (defined? dynamic-link)
> ERROR: In procedure defined? in expression (defined? dynamic-link):
> ERROR: Wrong type argument in position 1: #<primitive-procedure
> dynamic-link>
> ABORT: (wrong-type-arg)

No.  `define?' is a normal procedure and you have to pass it a symbol.

`defined?' could be defined like this

    (define (defined? symbol)
      (module-defined? (current-module) symbol))

I suggest you use `module-defined?' directly to be explicit about the
module issues.  Using the current-module is probably not what you want
most of the time.

The current-module is the module that is current when the code is
*evaluated*, not the module in which it is defined.  You probably want
to use the current-module only at the top-level, or when working in
the innards of the module system itself.

A typical use is maybe

    (define-module (my module)
      :use-module (his module))

    (define my-module (current-module))

    (define (foo)
      (if (module-defined? my-module 'bar)
          (do-something-with bar)))

Using `defined?' would not be the same thing, because the
current-module can be anything when foo is evaluated.