[Haskell-beginners] comment on this debugging trick?

Dennis Raddle dennis.raddle at gmail.com
Sun Nov 29 08:02:51 UTC 2015

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

> 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.
Thanks for the pointers, Stephen. I will look into it. I don't know if I'll
have time to learn how to do this though. I'll keep it in mind for the

This is a small, ongoing, no-pressure project, which is even lower pressure
when you consider I'm using what I call "just in time" debugging and
design. When I look at my use cases, I don't implement any that seem
unlikely. If they ever do occur, I can deal with them then. But I don't
just ignore cases willy-nilly -- I always consider if they do occur, that
the resulting bug will be obvious right away and lead me directly to the

This is interesting when dealing with music playback. Some unexpected cases
won't give an error message but will affect the playback sound -- so I
always ask myself, "Will this bug be obvious, really screw up the sound in
a major way, so I know it's happening?" Because what I don't want are bugs
that create small effects that I might miss for a while so I miss the
critical moment they were introduced.

I don't know the definition of the different processes but does "Just In
Time" design/debugging have something to do with Agile?

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