Oh golly. I can't live without pattern guards. they are the best darn thing since sliced bread. I highly recommend them. I .. would have to seriously refactor a ton of code if pattern guards disapeared.
So much so that it would be less work to implement pattern guards for other compilers and submit the patches.
eh, well, pattern guards are nice. but, many of their uses are also easily replaced, by moving the pg-monad from the lhs to the rhs, and employing MonadPlus for the fall-throughs; something roughly like: f p1 | g1 = e1 .. f pn | gn = en where <stuff> --> f x = fromJust $ do {p1 <- return x; guard g1; return e1} .. `mplus` do {pn <- return x; guard gn; return en} where <stuff> for any pattern matches in the guards, just drop the "guard";-) grouping several guards under one pattern is also straightforward. the only problem is where to place any pattern-dependent wheres. the easy approach matches them lazily out of x, but that matches some things twice.. this is not an argument against pattern guards; but I often find to my surprise that many Haskellers still think that functions with several clauses can't be translated easily (without losing the basic structure [*]) because of the "fall-through" on pattern-match failure, so they might find this translation pattern useful; it could also be elaborated (recovering better error messages) into a naive, but readable, desugaring of pattern-guards and the like, for reports, and for not-yet-supporting implementations.. cheers, claus [*] to be more accurate, since you can move the whole group of clauses into a case, the barrier is seen between moving from the world of patterns and guards to the world of expressions. MonadPlus allows us to move back.