Camlp4 help

[Andre Nathan <andre@sneakymustard.com>]

Hello

I'm just beginning with camlp4 here, and I'm stuck with what I think is
a precedence issue. I have the following syntax extension:

open Camlp4.PreCast
open Syntax

let sum = Gram.Entry.mk "sum"

EXTEND Gram
  expr: LEVEL "top"
    [ [ "sum"; "do"; seq = LIST1 sum; "done" ->
        <:expr< do { $list:seq$ } >> ] ]
    ;
  sum:
    [ [ x = expr; "plus"; y = expr ->
        <:expr< $x$ + $y$ >> ] ]
    ;
END

This works fine for something like this:

sum do
  1 plus 2
done

which becomes (1 + 2).

However, it breaks on

sum do
  let a = 1 in
  let b = 2 in
  a plus b
done

because it becomes ((let a = 1 in let b = 2 in a) + b).

How can fix that (allowing "b" to be in scope for the second argument of
"plus")?

Also, sequences of operations don't parse:

sum do
  1 + 2;
  3 + 4
done

gives "Parse error: [sum] or "done" expected (in [expr])"

What am I missing here?

Thanks in advance,
Andre