Bad ssyntax: a!
In the process I've also tightened up ssyntax in general, so that prefix/postfix ':' doesn't go through ssyntax expansion, etc. Some errors will now simply silently fail to transform.
Error: _a!: undefined
How do people feel about this?
Edit: I did this to reclaim scheme's '!' suffix for destructive operations, in particular for def and mac. A brief prior discussion about this: http://arclanguage.org/item?id=12505