[Caml-list] Define parser and printer consistently

[Dawid Toton]

I'm going to define a parser and a printer for a simple grammar.
Is there a way to define both of them in a single construct using some
existing OCaml tool?

For example, I have a keyword "function". The usual parser would contain
a mapping like:
"function" -> `Function
and the straightforward printer would do:
`Function -> "function"

What is the best way to combine these definitions, so that duplication
would be minimized?
To be precise, avoiding duplication is not exactly what I need. I'm
looking for something that would prevent making inconsistent changes to
the parser and the printer.

Dawid

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[Ashish Agarwal]

Maybe you will find Pickler Combinators useful:
http://research.microsoft.com/en-us/um/people/akenn/fun/picklercombinators.pdf

[Romain Bardou]

On 09/12/2010 05:47, Dawid Toton wrote:
> I'm going to define a parser and a printer for a simple grammar.
> Is there a way to define both of them in a single construct using some
> existing OCaml tool?
>
> For example, I have a keyword "function". The usual parser would contain
> a mapping like:
> "function" -> `Function
> and the straightforward printer would do:
> `Function -> "function"
>
> What is the best way to combine these definitions, so that duplication
> would be minimized?
> To be precise, avoiding duplication is not exactly what I need. I'm
> looking for something that would prevent making inconsistent changes to
> the parser and the printer.

I'm writing a tool called Parsini which, maybe, does what you're looking
for. Parsini stands either for "parsing is not interesting" (i.e.: let's
have a tool which does it quickly for us and move on to interesting
things such as code generation) or for "parser houdini" or something :p

From a simple grammar, the tool :
- infers and produces an AST ;
- produces an ocamlyacc source ;
- produces an ocamllex source (optional - you can use your own lexer) ;
- produces a main file with :
* functions to read your main entries easily from a channel, a file,
a string...
* functions to pretty-print your AST.
Your AST is pretty-printed with the Ocaml syntax, not the syntax of your
own language, which I do not know how to do.

I have not released the tool yet, so nothing is official nor documented
but you might want to take a look. License will be BSD. I've copied the
darcs repository on my website :

http://romain.bardou.fr/parsini

So you should be able to download it easily with :

darcs get http://romain.bardou.fr/parsini

Have fun,

--
Romain Bardou

[Yitzhak Mandelbaum]

PADS/ML can do that for you, and more. You can find information about the PADS languages and tools here:

http://www.padsproj.org

including papers and a manual. The website doesn't have the most recent release of PADS/ML -- i plan to put it up on Github shortly -- but if you're interested, i'm happy to send you a tarball.

The basic idea is that you specify your grammar as a type-like declaration. Then, pads/ml generates an AST, parser, printer and some more stuff for you. The generated parser is like a PEG parser, but with support context-sensitive parsing. That is, it is deterministic, with ordered choice; and, it is scannerless. So, the grammars-writing style has some significant differences from ocamllex and ocamlyacc.

PADS/ML has an Eclipse license.

Cheers,
Yitzhak

-----------------------------
Yitzhak Mandelbaum