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Date: Sat, 02 Nov 2013 19:57:11 +0000
From: Matej Kosik <5764c029b688c1c0d24a2e97cd764f@gmail.com>
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Subject: [Caml-list] camlp4: a silly question about quoting Ocaml terms

Hello,

According to various sources, Ocaml provides convenient means for generating Ocaml AST.
Yesterday I decided to look into the matter.

Now I am trying to generate a record type.

To certain point, things make sense. This:

  <:ctyp<{foo1:bar1; foo2:bar2}>>

is expanded to

    Ast.TyRec (_loc,
      (Ast.TySem (_loc,
         (Ast.TyCol (_loc,
                     (Ast.TyId (_loc, (Ast.IdLid (_loc, "foo1")))),
                     (Ast.TyId (_loc, (Ast.IdLid (_loc, "bar1")))))),
         (Ast.TyCol (_loc,
                     (Ast.TyId (_loc, (Ast.IdLid (_loc, "foo2")))),
                     (Ast.TyId (_loc, (Ast.IdLid (_loc, "bar2")))))))))

By looking at:

  http://brion.inria.fr/gallium/index.php/Abstract_Syntax_Tree#Types

there is a line:

     <:ctyp< t : t >>	....... Field declaration ........ TyCol of Loc.t and ctyp and ctyp

so it seems that it should also be somehow posible to get a quote for "field declaration", i.e.:

  <:ctyp<foo1:bar1>>

However, if I try that, I get an error:

  While expanding quotation "ctyp" in a position of "expr":
    Parse error: "->" expected after [ctyp level star] (in [ctyp]

I do not quite understand why that quotation was rejected by camlp4.

Of course, it is perfectly possible to write:

  Ast.TyCol (_loc,
             (Ast.TyId (_loc, (Ast.IdLid (_loc, field_name)))),
             field_type

but I am wondering whether there is a more intelligent way to do that
(e.g. <:ctyp<foo1:bar1>> or something like that).

---

As always, thank you in advance for your kind help.