Re: [Chicken-hackers] expand seems not to keep the promise made in the manual

[Kon Lovett]

On May 23, 2013, at 3:32 AM, Peter Bex <address@hidden> wrote:

> On Thu, May 23, 2013 at 11:59:44AM +0200, Christian Kellermann wrote:
>> Hi Joerg!
>> 
>> * Jörg F. Wittenberger <address@hidden> [130523 11:51]:
>>> Citing the manual
>>> 
>>>> <procedure>(expand X)</procedure>
>>> 
>>>> If {{X}} is a macro-form, expand the macro (and repeat expansion
>>>> until expression is a non-macro form).  Returns the resulting expression.
>> 
>> I think this is just wrong in the documentation. What you probably
>> want is expand* from the expand-full egg.
> 

I wrote expand-full for debugging my macros. That is why it installs a csi 
command. I never thought of it as useful in macro writing.

I need to change the documentation to note the limitations so people do not 
waste their time.

> Indeed.  However, it has to be noted that this egg is fundamentally
> broken: it has no access to the syntactic environment, so it can never
> do a proper job.  A trivial example of this kind of breakage follows:
> 
> (let-syntax ((foo (syntax-rules () ((_ x) x)))) (expand* '(foo 1))) =>
> (foo 1)
> 
> Hairier macros which contain renamed identifiers will also break.
> Actually, I've never found any use for expand-full except the most
> trivial of macros (the kind where you don't tend to need expand in
> the first place).
> 
> I don't think this is fixable, but I'd love to be proven wrong.
> 
> Cheers,
> Peter
> -- 
> http://www.more-magic.net
> 
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