By "it can't be parsed to an AST" I meant "it can't be parsed to a useful AST used to run or generate code" on its own, it needs to be disambiguated through contextual information before anything can be done with the prospective subtree. Sorry for the lack of clarity.

> It's called an ambiguous grammar, which can still be context free.

The only way to disambiguate is to provide expression context (namely visible name bindings at this point), it's essentially the same problem Eli Bendersky described when talking about C grammar's context-sensitivity: http://eli.thegreenplace.net/2007/11/24/the-context-sensitiv...