]> Thanks for your detailed reply. I had a suspicion I would have to read the source code to get the all of the necessary documentation. However, I'm still missing some basic point here. On Wed, Oct 7, 2009 at 4:16 PM, blue storm <bluestorm.dylc@gmail.com> wrote: > The different "level names" are not absolute among all camlp4 grammars > : they're a property of each grammar rule of each grammar. If you want > to "modify" a specific grammar (that is, EXTEND it), you must check > the different levels available in the definition. Yes, I understand that. But how do you specify which grammar your file is extending? My file is structured like this: #load "pa_extend.cmo"; #load "q_MLast.cmo"; open Pcaml; EXTEND GLOBAL: expr; ... END; So where did I specify whether I was extending the original syntax or the revised syntax (or some other grammar entirely)? I suppose I must have implicitly chosen the original syntax because my code works fine on that. > While concrete syntaxes for revised and classical syntax are > different, the abstract syntax tree is the same. Camlp4 quotations > works by replacing (using camlp4) the quotation you wrote by the > concrete ocaml AST representation. Yes, this point is crystal clear, and I have no problem writing the quotations in the revised syntax. > In your specific case, you can parse whatever syntax you want using > the "<-" operator, then output the corresponding AST using a quotation > in the revised syntax, that is <:expr< a := b >> (instead of "a <- > b"). For a reference, see the related rules in etc/pa_o.ml : > >  | ":=" NONA >    [ e1 = SELF; ":="; e2 = expr LEVEL "expr1" -> >      <:expr< $e1$.val := $e2$ >> >    | e1 = SELF; "<-"; e2 = expr LEVEL "expr1" -> >      <:expr< $e1$ := $e2$ >> ] Thanks, I found this piece of code. Now on a more specific point, I am confused about the parsing of record access and update: 1) In the parsing rule for the simple dot noation... | e1 = SELF; "."; e2 = SELF -> <:expr< $e1$ . $e2$ >> ] ...why is the field label an "expr"? This does not agree with the OCaml manual, which has a separate syntactic category for "field" (http://caml.inria.fr/pub/docs/manual-ocaml/expr.html), nor with my intuition about the meaning of the code. 2) Furthermore, as one can see from the ":=" entry above, the entire left side of a record update is parsed as its own subexpression. So this means, that in the context of a record update, that subexpression has to be interpreted as a reference, but in other contexts, the very same expression must be interpreted as a value. I don't necessarily care what kind of magic makes this possible on the back end, but I am wondering whether this has any implications for modifying the record syntax. - Aaron