I've written a few Pratt parsers in my time. You don't need a lexer and you can have more parser states than are implied by 'nud' and 'led'. They can be incredibly extensible. For example, if you can parse the expression "{a:1, b:2}" then you might naturally have an Expr state (nud), a Between state (led) and a DictKey state; that might initially accept just an identifier and a colon before recursing into Expr state, but you could later add dynamic expressions, perhaps via a macro, to support [expr] as a key.