Re: [Caml-list] Implementing include "file" statement in menhir

["François Pottier" <francois.pottier@inria.fr>]

Hello,

On 21/01/2020 07:48, Richard W.M. Jones wrote:
> I'm writing a parser which needs to have a C-like include directive.
> I thought I'd have a go at writing an include statement in menhir, and
> I did come up with something which works but it's quite a large hack.

If it is OK to recognize and obey an "include" directive in every 
grammatical
context (as opposed to only where a valid "stmt" is expected) then I would
suggest implementing support for "include" at the level of the lexer, so the
parser is entirely unaware of it. (I haven't tried it, though; it might take
some thought to come up with an approach that does not involve horrible side
effects.)

If on the contrary you wish to consider "include <foo.h>" as a valid 
statement
(and be able in principle to parse what follows without actually reading the
file foo.h) then I would suggest making Include a constructor in the 
abstract
syntax tree and defer reading included files to a separate "include
resolution" pass (which is allowed to invoke the parser). This approach 
should
be conceptually simpler. Disadvantages: 1- it should be slower by a constant
factor; 2- the include resolution pass requires writing a lot of boilerplate
traversal code (but this could be automated using the visitors package).

> How do you pass extra parameters to menhir's generated parser functions?

If you need to parameterize the entire parser, you can use %parameter 
(see the
manual, section 4.1.2).

If you need to parameterize only certain semantic actions, then you can let
these semantic actions return a closure, as in { fun my_parameter -> ... }

> Is there a nice way to export values into menhir's generated parser.mli
> file?

No. If you would like to write some code by hand and make it visible in
an .mli file, then you must write a separate module.

Hope this helps,

--
François Pottier
francois.pottier@inria.fr
http://gallium.inria.fr/~fpottier/