Quotations and the functorial camlp4 interface

Quotations and the functorial camlp4 interface

[Hendrik Tews]

Hi,

Camlp4 parsers have a functorial interface (eg.
Camlp4OCamlParser.Make), which makes it possible to build two
camlp4 syntax modules in one application that parse different
syntaxes. 

How can I add quotation support to such camlp4 parsing modules?
[Unfortunately, there is no functor
Camlp4OCamlRevisedQuotationExpander.Make.]

More in detail: Assume I obtained two camlp4 syntax modules SO
and SR, such that SO parses the orginal syntax and SR parses the
revised syntax. I now want to add quotation support to both SO
and SR. Following Camlp4OCamlRevisedQuotationExpander I do

  module PreCast = Camlp4.PreCast
  module type Camlp4Syntax = Camlp4.Sig.Camlp4Syntax 
    with module Loc = PreCast.Loc
    and module Ast = PreCast.Ast

  module Make
    (HostSyntax : Camlp4Syntax)
    (MakeQuotationSyntax : functor(EmptySyntax : Camlp4Syntax) -> Camlp4Syntax) 
    =
  struct
    module Gram = PreCast.MakeGram(PreCast.Lexer)
    module EmptySyntax = 
      Camlp4.OCamlInitSyntax.Make(PreCast.Ast)(Gram)(HostSyntax.Quotation)
    module QuotationSyntax = MakeQuotationSyntax(EmptySyntax)
    module X = 
      Camlp4QuotationCommon.Make(QuotationSyntax)(HostSyntax.AntiquotSyntax)
  end

now I can add the quotation support to SO and SR with

  let module M = Make(SO)(Camlp4OCamlRevisedParser.Make) in
  let module M = Make(SR)(Camlp4OCamlRevisedParser.Make) in
  ()

Could anybody comment on this?

The solution above is based on the following observations:

1. Camlp4QuotationCommon.Make(QuotationSyntax)(..) installs the
   parser in QuotationSyntax as (various) quotation expander(s)
   in QS.Quotation. This has only an effect on HostSyntax if the
   references that Camlp4QuotationCommon.Make mutates are
   actually identical in QuotationSyntax and HostSyntax.

2. The two MakeQuotationSyntax candidates
   Camlp4OCamlRevisedParser.Make and Camlp4OCamlParser.Make do
   only mutate the grammar entries in their argument modules.
   Therefore one always has to create new EmptySyntax'es but can
   reuse all the rest (especially Lexer, Ast and Loc) from
   Camlp4.PreCast.

3. The functor Camlp4QuotationExpander.Make cannot be used
   instead of Make above, because it creates reflective grammers
   (where the host syntax and the quotation syntax are
   identical).

Are these observations right?

Finally I have the following question:

4. Why does Camlp4OCamlRevisedQuotationExpander generate a new
   grammar module Gram and does not reuse Camlp4.PreCast.Gram?
   Can the latter be changed by some syntax extension?


[This post actually belongs to the thread
http://caml.inria.fr/pub/ml-archives/caml-list/2008/04/9d32f304eec6328db7ce857673842760.en.html,
which discusses how to make those functors SO and SR.]

Bye,

Hendrik Tews

Re: [Caml-list] Quotations and the functorial camlp4 interface

[Hendrik Tews]

I wrote:

   More in detail: Assume I obtained two camlp4 syntax modules SO
   and SR, such that SO parses the orginal syntax and SR parses the
   revised syntax. I now want to add quotation support to both SO
   and SR. Following Camlp4OCamlRevisedQuotationExpander I do

There is one point that I found out myself in the meantime:
quotations are installed by mutating something inside the
Quotation submodule of a Camlp4Syntax. Further, the functor that
creates emoty syntaxes, OCamlInitSyntax, uses its Quotation
argument literally as Quotation submodule in its output.
Therefore, when creating the modules SO and SR it is important to
do so with freshly generated quotations modules (by
Camlp4.Struct.Quotation.Make).

How about the Loc submodule of Ast that is passed into
OCamlInitSyntax? There is the mutable Loc.name, which contains
the default location variable. If I reuse the Ast argument of
OCamlInitSyntax, will the mutable Loc.name be shared between the
outputs? Are there syntax extensions in the camlp4 distribution
that mutate Loc.name?

Bye,

Hendrik

Re: [Caml-list] Quotations and the functorial camlp4 interface

[Hendrik Tews]

I wrote:

   How about the Loc submodule of Ast that is passed into
   OCamlInitSyntax? There is the mutable Loc.name, which contains
   the default location variable. If I reuse the Ast argument of
   OCamlInitSyntax, will the mutable Loc.name be shared between the
   outputs? 

Yes, it will, changing Loc.name has a global effect. 

What's more problematic is that the Loc sources are not
functorized, that is, there is only one instance
(Camlp4.Struct.Loc) that one can use. Consequently, Loc.name is a
kind of global Camlp4 reference, similar to
Camlp4_config.quotation and Camlp4_config.antiquotations.

   Are there syntax extensions in the camlp4 distribution
   that mutate Loc.name?

A grep for Loc.name yields only one place that changes Loc.name:
the option -loc in Camlp4Bin.ml. So the answer is probably no.

Bye,

Hendrik

Re: [Caml-list] Quotations and the functorial camlp4 interface

[Hendrik Tews]

Hi,

I have another comment in this speek-to-myself-thread:

I wrote:

   2. The two MakeQuotationSyntax candidates
      Camlp4OCamlRevisedParser.Make and Camlp4OCamlParser.Make do
      only mutate the grammar entries in their argument modules.

This is wrong: When they extend the syntax they register
keywords, which are apparently stored in a hash table in the
grammar module. Therefore they mutate the grammar module.

      Therefore one always has to create new EmptySyntax'es but can
      reuse all the rest (especially Lexer, Ast and Loc) from
      Camlp4.PreCast.

At least the grammar argument to OCamlInitSyntax should always be
freshly generated by
Camlp4.Struct.Grammar.Static.Make(Camlp4.PreCast.Lexer) to start
with a fresh keyword hash.

   4. Why does Camlp4OCamlRevisedQuotationExpander generate a new
      grammar module Gram and does not reuse Camlp4.PreCast.Gram?
      Can the latter be changed by some syntax extension?

This is answered now.

Bye,

Hendrik