Re: [Chicken-users] A few questions

[Kon Lovett]

On Jan 29, 2008, at 9:47 AM, Hans Nowak wrote:

> Hi,
>
> I am studying Chicken this year (and blogging about it, as some  
> people here
> already discovered :-).  So far I have been able to figure out most  
> things by
> myself (my experience with Scheme is limited, but I'm not a *complete*
> beginner), but I still have a few unanswered questions.  Maybe  
> somebody here
> can help me.  Here goes...
>
> 1. Does Chicken (or Scheme in general) support docstrings?

Chicken doesn't; this is an on-going issue/discussion. Scheme, in the  
sense of RnRS, doesn't. Some Scheme implementations might.

Common LISP does but that isn't a Scheme.

> 2. Python has a way to make the same file usable as both a module  
> and a
> script. For example:
>
>   # foo.py
>
>   def bar(x): ...
>
>   if __name__ == "__main__":
>       bar(42)
>
> When run as a script, all the code is executed; when imported, you  
> get the
> definitions, but the code inside the 'if' is omitted.
>
> Is there a way to do something similar in Chicken?  Or, in other  
> words, is
> there a way for Chicken code to tell if it's being run a script, or  
> being
> loaded as auxiliary code?

For interpreted code, see
http://galinha.ucpel.tche.br/A%20script%20to%20browse%20the%20HTML% 
20manual

For compiled code, not without some work. An extension can be created  
(a dynld binary). Then create a program (a binary) that uses the  
extension & parses the command line and calls the extension's  
procedures. See http://galinha.ucpel.tche.br/chicken-setup

> 3. This is more of a technical question about something that I  
> haven't grasped
> yet.  When I define a function, I can "see" it at the toplevel, and  
> refer to
> it by name:
>
>   #;8> (define (f x) x)
>   #;9> f
>   #<procedure (f x)>
>
> But I cannot do the same thing with macros:
>
>   #;6> (define-macro (m x) `,x)
>   #;7> (m 3)
>   3
>   #;8> m
> Error: unbound variable: m
>
> Why is that?  There is probably a good reason why I cannot type 'm'  
> and get
> back something like '#<macro (m x)>', but what is that reason?

Different "namespace". However the macro "namespace" & the toplevel  
"namespace" shadow each other:

#;1> (define foo 1)
#;2> foo
1
#;3> (define-macro (foo) 1)
#;4> (foo)
1
#;5> (define foo 1)
#;6> foo
1
#;7> (foo)
Error: call of non-procedure: 1

        Call history:

        <syntax>                (foo)
        <eval>          (foo)   <--


> Also, is there
> a way to get a list of defined macros?

In the utils unit the apropos functions can list macros. However,  
these take a pattern and are not exclusive to macros - procedures are  
included.

An undocumented function can be used to just list the macros -  
(##sys#apropos-macros "" #f).

I don't think hygienic macros will be listed.

> Thanks,
>
> --Hans
> `
>
>
>
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Best Wishes,
Kon