[Haskell-beginners] comment on this debugging trick?

[Jeffrey Brown]

>  (Parsec, Attoparsec, ...) can't
> be used with XML.Light because their mechanics are consuming
> an input stream whereas processing XML (or JSON) is
> moving a cursor through a tree

Stephen, the "consuming an input vs. moving a cursor through a tree"
distinction you're drawing is unclear to me. Can you elaborate, or provide
references?

Also, Text.JSON.Parsec [1] would appear to be a counterexample to your
claim.

[1]
https://hackage.haskell.org/package/json-0.9.1/docs/Text-JSON-Parsec.html

On Sat, Nov 28, 2015 at 2:14 AM, Stephen Tetley <stephen.tetley at gmail.com>
wrote:

> Hi Dennis
>
> For this use case I would make a small, general parser combinator
> library / monad on top of XML.Light, then use the new parser
> combinators to make a specialized parser for your subset MusicXML.
>
> The common parser combinator libraries (Parsec, Attoparsec, ...) can't
> be used with XML.Light because their mechanics are consuming an input
> stream whereas processing XML (or JSON) is moving a cursor through a
> tree, but the common API provided by parser combinator libraries can
> be re-used productively for a tree (cursor) parser. As well as moving
> the cursor, the custom parser monad can handle errors and backtracking
> if needed.
>
> Best wishes
>
> Stephen
>
> On 27 November 2015 at 23:55, Dennis Raddle <dennis.raddle at gmail.com>
> wrote:
> >
> >
> [snip]
> >
> >
> > I've used the Either monad for exception handling. Yes, I was using do
> > notation. This current project is just for myself. Exceptions represent
> > either bugs or malformed input. I can catch some of them in the IO monad
> so
> > my program prints an error but keeps running and lets me try again. If
> the
> > program crashes out, no big problem.
> >
> > I'm parsing MusicXML with Text.XML.Light. The XML is always well-formed.
> > However *MusicXML* is not a well-defined language. Like, does every
> <note>
> > element have a child element called <voice>? No guarantee I can find,
> yet it
> > has been true in the examples I've tried with the only typesetter I'm
> using
> > to generate MusicXML.  I can get my program running quickly without
> > bothering with the case that <voice> is absent. But if that case someday
> > occurs, I want to know precisely and immediately. Yet I don't want to
> write
> > a detailed error message for every violated assumption, of which there
> are
> > dozens necessary. So my solution is to find these things with case
> > exhaustions. The program crashes and I have to inspect the code, but no
> > problem.
> >
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>



-- 
Jeffrey Benjamin Brown
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/beginners/attachments/20151128/90401c31/attachment.html>