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Date: -- (:)
From: Andre Nathan <andre@s...>
Subject: Re: [Caml-list] Camlp4 help
Hi

On Sat, 2009-03-21 at 16:26 +0100, blue storm wrote:
> This is not a camlp4-specific problem : the grammar you described
> apparently do not conform to what you have in mind.

I think I understand, although I thought the "x = expr" rule in the sum
form definition meant that before "plus" any expression would be
allowed.

I want to allow any expression inside a "sum" block, which I think I
could do by defining it as a new rule in "expr", but I'd like "plus"
expressions to only be allowed inside a "sum" block, which I'm not sure
how to do.

Thanks,
Andre

> 
> According to your definition, the "sum do ... done" can only contain
> "sum" forms, not an arbitrary expression. The only valid way to parse
> "sum do let a = b in a plus c done" is thus "sum do (let a = b in a)
> plus b done", as "sum do let a = b in (a plus b) done" has an
> expression (instead of a sum) between do ... done (and a sum in expr
> position, wich is also incorrect, but it can also be parsed as a
> correct expression).
> 
> What is the syntax you want to be supported ?
> 
> On 3/21/09, Andre Nathan <andre@sneakymustard.com> wrote:
> > 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
> >
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> 
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