The SyntaxError is actually caused by a bug in the parser code! When s_push() reports a stack overflow it returns -1, which is passed through unchanged by push() -- but the code that calls it only checks for positive error codes! I've fixed this by returning E_NOMEM from s_push() instead.

The only downside I see of making MAXSTACK larger is that a stack of maximal size is allocated each time the parser is invoked. With MAXSTACK=500 on a 32-bit machine, that's 6K. Switch to 5000 and it's 60K. No big deal except perhaps for ports to PalmPilots and the like...

Note that with MAXSTACK=500, you can "only" have 35 nested lists.