Specialize sequence into sequence_ automatically
Currently, every function that has a useful "effect" as well as a potentially large result value, needs to get two implementations: One that accumulates the result in memory and yields it, and one that avoids accumulating it in the first place.
sequence vs. sequence_
mapM vs. mapM_
Parsec's: many vs. skipMany
Now that I am writing parser combinators, I'm finding that I need a "skip" version of each parser I write, if my parser has a large value.
If GHC can detect whether a value is eventually used, it could specialize sequence into sequence_ automatically, when it notices that the list is unused.