[Haskell-cafe] Re: [Haskell] View patterns in GHC: Request forfeedback

[Jacques Carette]

Others have already pointed this out, but it is worth saying again: 
Maybe is not the only monadic effect which makes sense during 
pattern-matching.  Wolfram Kahl and I have explored some of these things 
as part of the Pattern Matching Calculus,
http://sqrl.mcmaster.ca/~kahl/PMC/
[If you want to jump to the most recent, most complete version, see
http://www.cas.mcmaster.ca/~kahl/Publications/TR/Kahl-Carette-Ji-2006b/]

Various other monads can be used for pattern-matching-effects.  While 
Maybe is quite classical, List and LogicT give extremely useful 
alternatives.

Jacques