camlp4 infix let

camlp4 infix let

[Jacques Le Normand]

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Dear List,
I'm writing a camlp4 syntax extension and I'd like to write

    <:expr< let ( >>= ) = Bar.( >>= ) in 5 >>

but camlp4 complains:

      While expanding quotation "expr" in a position of "expr":
        Parse error: ")" or [ipatt] expected after "(" (in [ipatt])

yet it seems to be valid revised syntax. Does anyone have any ideas?

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Re: [Caml-list] camlp4 infix let

[Jérémie Dimino]

Hi,

Le mercredi 07 avril 2010 à 15:05 -0400, Jacques Le Normand a écrit :
> Dear List,
> I'm writing a camlp4 syntax extension and I'd like to write 
> 
>     <:expr< let ( >>= ) = Bar.( >>= ) in 5 >>
> 
> but camlp4 complains:
> 
>       While expanding quotation "expr" in a position of "expr":
>         Parse error: ")" or [ipatt] expected after "(" (in [ipatt])
> 
> yet it seems to be valid revised syntax. Does anyone have any ideas?

It is because the ">>" of the ">>=" operator is detected as the end of
the camlp4 quotation. You can try something like that:

   let operator = ">>=" in <:expr< let ($lid:operator$) = Bar.($lid:operator$) in 5 >>

Cheers,
Jérémie

Re: [Caml-list] camlp4 infix let

[Martin Jambon]

Jérémie Dimino wrote:
> Hi,
> 
> Le mercredi 07 avril 2010 à 15:05 -0400, Jacques Le Normand a écrit :
>> Dear List,
>> I'm writing a camlp4 syntax extension and I'd like to write 
>>
>>     <:expr< let ( >>= ) = Bar.( >>= ) in 5 >>
>> but camlp4 complains:
>>
>>       While expanding quotation "expr" in a position of "expr":
>>         Parse error: ")" or [ipatt] expected after "(" (in [ipatt])
>>
>> yet it seems to be valid revised syntax. Does anyone have any ideas?

The revised syntax of the old camlp4 or camlp5 requires a backslash in front
of the operator instead of parentheses:

$ cat foo.ml
let \>>= = Bar.\>>= in 5 ;

$ camlp5r pr_o.cmo foo.ml
let _ = let (>>=) = Bar.(>>=) in 5


I don't know how to make it work with the new camlp4:

$ camlp4r -printer o foo.ml
File "foo.ml", line 1, characters 4-8:
Parse error: "module" or [opt_rec] expected after "let" (in [expr])


> It is because the ">>" of the ">>=" operator is detected as the end of
> the camlp4 quotation. You can try something like that:
> 
>    let operator = ">>=" in <:expr< let ($lid:operator$) = Bar.($lid:operator$) in 5 >>

I would add it is simpler to just avoid << and >> in any ocaml source code
unless camlp5/camlp4 is not involved.


Martin

-- 
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