[plt-scheme] syntax-case and the name 'debug'

From: Matthew Flatt (mflatt at cs.utah.edu)
Date: Tue Oct 21 22:09:54 EDT 2003

At Wed, 22 Oct 2003 14:35:09 -0400 (EDT), Guillaume Marceau wrote:
> > (syntax-case (quote-syntax asd) ()
>     [(#%top . id) (debug "asd")]
>     [_ (debug 5)])
> STDIN::77: #%top: illegal use of syntax in: (#%top . debug)

This is certainly deeply confusing...

To simplify a little, and to show that "debug" is not special:

 >  (syntax-case not-even-evaluated ()
        [(#%top . any) xdebug])
 repl-1:2:21: #%top: illegal use of syntax in: (#%top . xdebug)

The problem is that xdebug is implictly wrapped with "#%top", like any
reference to a top-level variable. But the implicit "#%top" gets
captured by the syntax binding in the pattern!

I think it's likely that you meant to list `#%top' as a literal.
Otherwise, you can just pick a different name for the pattern. (Either
will avoid the problem.)


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