[Caml-list] A question about Camlp4

[Caml-list] A question about Camlp4

[Frederic Tronel]

Hi list,


I'm using camlp4 in order to embed a scripting language within my caml 
programs.
I've already done this one year ago for a subset of Lotos verification 
language, and I'm extending this work.

I'm facing a difficulty. Here is a canonical example of the problem:

EXTEND:
    rule1: ..... ->    <:expr< >>   (* A rule that generate a ML AST *)
    rule2:  OPT a = rule1 ..... ->
	let b = match a with
		None -> <:expr<None>>
		Some x -> <:expr<Some $x>>
	in
	<:expr< ATypeConstructor  $b$>>
...
END	

I have to do this small trick for each optionnal symbol in each rule, 
(this is also true for list meta symbols introduced by LIST0, LIST1 ...).
It would greatly improve readability of my program, if I could define a 
small function outside from the grammar extension which would do:

optionToAst o =
match o with
  None -> <:expr<None>>
  Some x -> <:expr<Some $x>>

However if I do this the compiler complains about unbound value "loc".
Thanks for your help.

Best regards,

Frederic Tronel.


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Re: [Caml-list] A question about Camlp4

[Remi Vanicat]

Frederic Tronel <Frederic.Tronel@inrialpes.fr> writes:

> Hi list,
>
>
> I'm using camlp4 in order to embed a scripting language within my caml
> programs.
> I've already done this one year ago for a subset of Lotos verification
> language, and I'm extending this work.
>
> I'm facing a difficulty. Here is a canonical example of the problem:
>
> EXTEND:
>     rule1: ..... ->    <:expr< >>   (* A rule that generate a ML AST *)
>     rule2:  OPT a = rule1 ..... ->
> 	let b = match a with
> 		None -> <:expr<None>>
> 		Some x -> <:expr<Some $x>>
> 	in
> 	<:expr< ATypeConstructor  $b$>>
> ...
> END	
>
> I have to do this small trick for each optionnal symbol in each rule,
> (this is also true for list meta symbols introduced by LIST0, LIST1
> ...).
> It would greatly improve readability of my program, if I could define
> a small function outside from the grammar extension which would do:
>
> optionToAst o =
> match o with
>   None -> <:expr<None>>
>   Some x -> <:expr<Some $x>>
>
> However if I do this the compiler complains about unbound value "loc".
> Thanks for your help.


there is an "hidden" loc "argument" to expr quotation, and this loc
variable is defined in the action.

let optionToAst loc o =
match o with
| None -> <:expr<None>>
| Some x -> <:expr<Some $x>>

then you could call "optionToAst loc a" and it will work...

-- 
Rémi Vanicat
vanicat@labri.u-bordeaux.fr
http://dept-info.labri.u-bordeaux.fr/~vanicat

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Re: [Caml-list] A question about Camlp4

[Frederic Tronel]

Remi Vanicat wrote:

> 
> there is an "hidden" loc "argument" to expr quotation, and this loc
> variable is defined in the action.
> 
> let optionToAst loc o =
> match o with
> | None -> <:expr<None>>
> | Some x -> <:expr<Some $x>>
> 
> then you could call "optionToAst loc a" and it will work...


Thank you, it does work.
Is it documented somewhere ? (I know that "loc" is used in the source 
location).


Best regards,

Frederic.




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Re: [Caml-list] A question about Camlp4

[Frederic Tronel]

> 
> 
> # let f a loc = <:expr< { a=$a$; b="toto"} >>;;
>                            ^^
> While expanding quotation "expr":
> Parse error: [fun_binding] expected after [patt_label_ident] (in
>   [label_expr])
> # let f a loc = <:expr< { a = $a$; b="toto"} >>;;
> val f : MLast.expr -> MLast.loc -> MLast.expr = <fun>
> 
> c'est subtil, mais pas vraiment un bug (le problème est que =$ peut
> être définit en caml...
> 
> [...]
> 
> 


merci, voila qui clos le thread :)


Frederic


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