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camlp4 stream parser syntax
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Date: -- (:)
From: Joel Reymont <joelr1@g...>
Subject: Re: Re : [Caml-list] Re: camlp4 stream parser syntax

On Mar 7, 2009, at 11:21 PM, Matthieu Wipliez wrote:

> why are you using stream parsers instead of Camlp4 grammars ?

Because I don't know any better? I'm just starting out, really.

I have a parser that I wrote using ocamlyacc and menhir. I finally  
when with dypgen and didn't touch the code for a few months. I then  
tried to simplify the grammar on account of a later type checking pass  
and realized that I cannot troubleshoot it.

I think I can make do with a camlp4 parser and it will vastly simplify  
debugging.

> This:
> ...
> could be written as:
> expression: [
>  [ (i, _) = INT -> Int i
>  | (s, _) = STRING -> Str s
>  ... ]
> ];

Doesn't your example assume that I'm using the camlp4 lexer?

> expression: [
>  [ e1 = SELF; "/"; e2 = SELF ->
>    if e2 = Int 0 then
>      Loc.raise _loc (Failure "division by zero")
>    else
>      BinaryOp (e1, Div, e2) ]
> ];

Where does SELF above come from?

Can I use a token instead of "/" since I return SLASH whenever "/" is  
found by the lexer.

> By the way, do you need you own tailor-made lexer? Camlp4 provides  
> one that might satisfy your needs.

It has been said that it's not extensible so I wrote my own lexer  
using ocamllex and wrapped it to return (tok, loc) Stream.t.

> Otherwise, you can always define your own lexer (I had to do that  
> for the project I'm working on, see file attached).

Thanks, I'll study it.


> Your parser would then look like
>
> (* functor application *)
> module Camlp4Loc = Camlp4.Struct.Loc
> module Lexer = Cal_lexer.Make(Camlp4Loc)
> module Gram = Camlp4.Struct.Grammar.Static.Make(Lexer)

Is this extending the OCaml grammar or starting with an "empty" one?

> (* rule definition *)
> let rule = Gram.Entry.mk "rule"

Is this the "start" rule of the parser?

	Thanks, Joel

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