[plt-scheme] displaying errors in custom language levels

> You're not getting any source locations in the error message because
> the code is not recording any source locations! 

Oh! All this time I thought I was adding source location information to 
syntax objects by rewrapping them with datum->syntax-object plus a 
source location syntax object -- hence the calls to (build-syntax 
#'whatever loc) -- but I guess the only way to do it is syntax/loc. Thanks.

> Forgetting about the recent changes to mzscheme to record procedure's
> locations, there is no built in way to record locations of errors. You
> have to implement it or use a library, like errortrace.

Okay.

> There are two basic techniques. Errortrace's (where information is
> recorded with continuation marks on all subexpressions, and extracted
> from the exception record by the error-display handler) and the one
> used by syntax errors (search for exn:srcloc in Help Desk).

Okay, thanks.

Dave