Re: [Caml-list] Partial parsing

[Fermin Reig <reig@acm.org>]

Markus Mottl wrote:
> Hi,
> 
> one feature that I'd love to see with our lexing/parsing tools for
> OCaml would be the possibility to perform partial lexing / parsing.
> 
> For example, imagine that you read a message from a socket into a
> string buffer, but it is not yet complete.  You may not be able to
> know that in advance, because that would require parsing it.
> 
> What I'd like to be able to do is to e.g. call a lexer or parser
> function on this buffer, and it will recognize as much as possible
> with the option to continue parsing in another buffer.  For this we
> could e.g. define a type "parse_result":
> 
>  type parse_result =
>    | Done of result * int
>    | Cont of parse_fun
>  and parse_fun = pos : int -> len : int -> string -> parse_result
> 
> If a full parse was detected, it would return e.g. "Done (result,
> next_pos)", where "result" is the result of the successful parse, and
> "next_pos" is the position in the buffer that contains the character
> following the successfully parsed text.
 > [...]

This sounds like a parsing problem suitable for the parser combinator 
approach. There, the result of a parse is a pair where one of the two 
components is the remaining of the input string.

Many of the papers and implementations are from the Haskell folk, but I 
think there are some in Ocaml as well.

HTH,
Fermin