[plt-dev] macro error messages

On 03/29/2010 03:19 PM, Matthew Flatt wrote:
> At Mon, 29 Mar 2010 15:06:00 -0600, Jon Rafkind wrote:
>    
>> Can these error messages be reviewed as well?
>>
>> On 03/26/2010 03:55 PM, Jon Rafkind wrote:
>>      
>>> Can this error message
>>>
>>>    illegal use of syntax
>>>
>>> be changed to
>>>
>>>    illegal application of a transformer. transformers must be functions
>>> that accept one argument.
>>>
>>> To reproduce this error use this code:
>>>
>>> (define-syntax (foo a b c) #'1)
>>> (foo)
>>>
>>> There is only one change to be made in eval.c line ~6284
>>>        
> Like the suggested `syntax-case' change, I think this one assumes the
> perspective of a macro implementor with a particular goal.
>
> In general, an identifier bound with `define-syntax' doesn't have to be
> bound to a transformer procedure. A non-transformer binding may be
> intentional and useful, such as when a pattern variable is bound by
> `syntax-case'.
>
> In such cases, it's a good idea to make the binding also include a
> transformer procedure (perhaps through `prop:procedure') and refine the
> "illegal use of syntax" error message --- just like it's a good idea to
> cover more cases in `syntax-case' or `syntax-parse' and give good error
> messages. But if a programmer doesn't do that, then "bad syntax" or
> "illegal use of syntax" is about all that can be said automatically.
>
>
>    

I don't follow you. The C code has a check to see if the thing being 
applied is a procedure with an arity of 1. If it is anything else, the 
error "illegal use of syntax" will be raised. So my suggestion is for 
the error message to mirror the check being done.