[plt-dev] at-exp and whitespace

From: Dave Herman (dherman at ccs.neu.edu)
Date: Fri Feb 27 08:50:46 EST 2009

I have a C parser that I would like to integrate with the at-exp  
reader so you can write things like

     #lang at-exp scheme/base
     (define decls
         typedef int foo;
         typedef char bar;

There's a subtle pitfall: if you insert whitespace between  
@declaration-list and the first curly brace (which is very tempting,  
given traditional C style), it reads as

     (define decls declaration-list {typedef int foo typedef char bar})

which is then a syntax error with `define'. There doesn't seem to be  
any way that the `declaration-list' macro can defend against this with  
a clearer error message.

As a compromise, would it make sense for the at-exp reader to turn off  
`read-curly-brace-as-paren' so that wherever an accidentally orphaned  
curly-brace argument appears, it can produce a more localized error?  
It's not a perfect solution, but curly braces are pretty rarely used  
as an S-expression delimiter so it might not be too bad of a compromise.


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