[Haskell-beginners] Writing an instance of Read?

Is there a tutorial - or anything at all, for that matter - on writing Read instances? Particularly so that it integrates properly types that incoporate your type and derive Read? Real World Haskell gives one simple example (which doesn't use the first argument), points out one problem with the example, then says "many people find it easier to use Parsec." And that's the best such I could find. Thanks, <mike -- Mike Meyer <mwm@mired.org> http://www.mired.org/ Independent Software developer/SCM consultant, email for more information. O< ascii ribbon campaign - stop html mail - www.asciiribbon.org