Then you don't need the lexer to parse balanced parens. The job of the lexer is to turn ("Foo(" + bar) into something like OpenParen String Op Identi

Then you don't need the lexer to parse balanced parens. The job of the lexer is to turn ("Foo(" + bar) into something like OpenParen String Op Identifier CloseParen Then the (synyactical) parser takes over. This is pretty standard.