Stream parsers, again

Stream parsers, again

[Frank A. Christoph]

Regarding my previous message, I just figured out that it is actually quite
easy to get "midstream" counts. Define this:

let count = parser bp [< >] -> bp

and then you can insert it in critical places like the example I gave:

  parser [< e = p; i = count; e' = p' ? err i >] -> ...

BTW, it is nice that the error expression is itself lazily evaluated. I
think it is too restrictive that it needs to return a string rather than an
arbitrary type, but fortunately you can just raise an exception from within
the stream error exception itself:

  exception Err of int
  let err cnt = raise (Err cnt)

--fac

Re: Stream parsers, again

[Daniel de Rauglaudre]

Hello,

On Tue, Feb 01, 2000 at 11:19:18AM +0900, Frank A. Christoph wrote:

> let count = parser bp [< >] -> bp

This function already exists: "Stream.count".

>   parser [< e = p; i = count; e' = p' ? err i >] -> ...
> 
> BTW, it is nice that the error expression is itself lazily evaluated.

If you got the name of the stream (i.e. "strm"), you can also use:

   parser [< e = p; e' = p' ? err (Stream.count strm) >] -> ...

> I think it is too restrictive that it needs to return a string
> rather than an arbitrary type

Mmm... Remember that polymorphic exceptions are impossible in Caml.
Your solution:

>   exception Err of int
>   let err cnt = raise (Err cnt)

... is the good one.

-- 
Daniel de RAUGLAUDRE
daniel.de_rauglaudre@inria.fr
http://cristal.inria.fr/~ddr/