[plt-dev] Re: [plt-scheme] New contract-related features

Thanks. That's progress! -- Matthias



On Feb 15, 2009, at 10:51 PM, Stevie Strickland wrote:

> On Feb 15, 2009, at 6:51 PM, Matthias Felleisen wrote:
>> I am sorry, but
>>
>>> Welcome to DrScheme, version 4.1.4.3-svn13feb2009 [3m].
>>> Language: Module; memory limit: 128 megabytes.
>>> . begin (possibly implicit): no expression after a sequence of  
>>> internal definitions in: ((define-syntax current-contract- 
>>> region11 (convert-renamer (λ (stx) (syntax (quote (region  
>>> f1)))))) (expand-ssp-body (current-contract-region1) (current- 
>>> contract-region11) (with-contract-helper #<procedure:syntax- 
>>> introducer> (quote (region f1)) ((g number?)) () (define g 10))))
>>> >
>>
>> is indefensible.
>
> Well, with the following patch, for:
>
>   (define (f x)
>     (with-contract f1
>       ((y number?))
>       (define y x)))
>
> I get:
>
>   begin (possibly implicit): no expression after a sequence of  
> internal definitions in: ((with-contract f1 ((y number?)) (define y  
> x)))
>
> However, I don't know the C internals well enough to know whether  
> this patch is good as-is or if there'd be any strange effects in  
> having just a straight alias like this and there's some bookkeeping  
> that'd need to be managed. It's just something I tried to see if  
> this is where such a change would need to be made.
>
> Stevie
>
> Index: src/mzscheme/src/eval.c
> ===================================================================
> --- src/mzscheme/src/eval.c	(revision 13652)
> +++ src/mzscheme/src/eval.c	(working copy)
> @@ -6313,7 +6313,7 @@
>     It is espcailly ugly because we have to expand macros
>     before deciding what we have. */
>  {
> -  Scheme_Object *first, *rib, *ctx, *ectx;
> +  Scheme_Object *first, *rib, *ctx, *ectx, *orig = forms;
>    Scheme_Comp_Env *xenv = NULL;
>    Scheme_Compile_Info recs[2];
>    DupCheckRecord r;
> @@ -6595,7 +6595,7 @@
>  	more = 0;
>        } else {
>  	/* Empty body: illegal. */
> -	scheme_wrong_syntax(scheme_begin_stx_string, NULL, forms,
> +	scheme_wrong_syntax(scheme_begin_stx_string, NULL, orig,
>  			    "no expression after a sequence of internal definitions");
>        }
>      }