[wg-camlp4] Meta Programming from the view of the implementaion

[Gabriel Scherer]

>>> What about nested uses of the same quotation?
>>>
>> Handled like nested comments, assuming the lexer knows where the
>> anti-quotations are.
>
> An assumption that I really don't think we should make. It involves forcing
> a particular style of anti-quotation on all extensions. Besides it is easier
> to simply use a syntax that supports unique delimiters.

Note that there is a nice continuum in the design space for
compromises between syntactic flexibility and easy tool support
(assuming non-smart, non-extensible tools that know how to handle
OCaml code):

0) Pure OCaml syntax : combinator libraries, etc. (note: this is where
the mixfix discussion fits)
1) Alain's style of all-OCaml expressions, using annotations to denote
the domain-specific semantics (tool support for the whole expression)
2) Quotations with an agreed-upon antiquotation syntax (tool support
inside antiquotations)
3) Quotations with extension-custom antiquotation syntax (no tool
support; treated like a string)

I would be interested in seeing which use cases can be satisfyingly
encoded under which approaches. I personally suspect that for
small-scale syntax supports (say, regexps), the outer quotation syntax
being too heavy is more problematic that any antiquotation syntax
considerations (because if it needs to be short it probably doesn't
have antiquotations besides possibly a custom syntax to denote OCaml
variables, that need no editor support).

(Note: to my knowledge, Hongbo was the first to remark (
http://caml.inria.fr/mantis/view.php?id=5665 ) that the Camlp4 syntax
for antiquotations was problematic for nested *antiquotations*. That's
a cogent point that can also be taken into consideration, and
something I like about his work on Fan. The use cases for this are
however quite specialized, so it will be easy to counter-argue that
those considerations are for the Fan-class of preprocessing, not the
included-in-the-language-itself one.)

On Thu, Jan 31, 2013 at 3:02 PM, Leo White <lpw25 at cam.ac.uk> wrote:
> On Jan 31 2013, Török Edwin wrote:
>
>> On 01/31/2013 03:56 PM, Leo White wrote:
>>>>
>>>> What do you think of this syntax:
>>>> {:lid|...|lid:}
>>>
>>>
>>> What about nested uses of the same quotation?
>>>
>>
>> Handled like nested comments, assuming the lexer knows where the
>> anti-quotations are.
>
>
> An assumption that I really don't think we should make. It involves forcing
> a particular style of anti-quotation on all extensions. Besides it is easier
> to simply use a syntax that supports unique delimiters.
>
>
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