As you might expect, the only solution that I found truly satisfying was the Haskell one :-)
Anyone who loves to browse voluminous manuals that describe huge inventories of library functions would agree with you, I'm sure. :)
... though this seems to be more of a library issue than a language one.
Exactly. If the implementation of Haskell's "group" function has the same parsimony and efficiency as the perl "while /regex/g" solution, and if I really need to use it often, then I would certainly prefer to use the function call (once I've discovered that it actually exists).
But if the "standard operators" provided by the language yield a fairly concise idiom for the task, why bother with the overhead (and relative obscurity) of a function call, especially if the particular task doesn't come up that often?