Re: [Caml-list] Problems with printing MetaOCaml generated code

[Jacques Carette <carette@mcmaster.ca>]

You will have some difficulties printing complex closures, especially 
when they refer to values built in the generator (CSPs) which are not 
simple values (strings, integers, etc).

Sometimes, very simple changes to the generator can allow closures and 
CSPs to be printable or not -- without very specific examples, I can't 
help (it's been a few years since I dug into this deeply).

I have been able to print rather complex, large codes with metaocaml.  
But one has to structure the generator rather carefully to ensure this 
possibility.

Jacques

On 2015-04-30 14:36 , Ömer Sinan Ağacan wrote:
> Hi all,
>
> I'm working on a MetaOCaml program and I want to save generated programs to
> files instead of directly running them within the same program using
> `Runcode.(.!)` or `Runcode.run`. The problem is MetaOCaml never prints
> generated code, it's always failing with `Warning 22: The CSP value is a
> closure or too deep to serialize`.
>
> I can't see anything related in it's web page:
> http://okmij.org/ftp/ML/MetaOCaml.html. What I understand from that page is
> once I have a closed code, I should be able to print it no matter what.
> However in my experience even the simplest realistic MetaOCaml program fails to
> generate the code because of this error I mentioned above.
>
> (One thing to note here is that my program generates the code on a couple of
> inputs, but fails in most of them with this error message.)
>
> In "Many ways to run the code" section it's said that "Since closed code is
> essentially OCaml AST, after closing the generated code, the user may examine
> and `run' it in many ways. One way of running the code is printing it." and
> then it lists some API functions for printing. In my experience none of them
> really work, I have closed code which I successfully closed using
> `Runcode.close_code`, but `print_closed_code` is still failing with the error,
> and `print_code_as_ast` is printing something that definitely doesn't look like
> an AST for any imaginable programming language.(okay... I might have
> exaggerated a bit, but it's definitely not OCaml AST and it contains some
> references to generator program source, like "Generator.ml[248]" for example)
>
> One relevant thing I could find in the documentation is this: "If the code
> includes CSP only as literals or external references (and any code can be
> arranged that way), the code can be stored into a file and then passed to
> ocamlopt." If we remove this sentence from the documentation, I don't think it
> mentions about any possible failures in code printing.
>
> So now that I've expressed my frustration about this, I guess my main question
> is: In what cases does MetaOCaml prints generated code? In what cases it
> doesn't? Note that it fails to generate code even after calling
> `print_closed_code (close_code ...)`, so being closed or not doesn't seem very
> relevent here. Is this a bug in MetaOCaml? Are there any workarounds? Any ideas
> what am I doing wrong?
>
> Thanks in advance for any answers,
>
> Ömer
>