On May 27, 2007, at 9:19 , Andrew Coppin wrote:
So... ∀x . P means that P holds for *all* x, and ∃ x . P means that x holds for *some* x? (More precisely, at least 1 possible choice of x.)
Exactly.
Seriously. Haskell seems to attract weird and wonderful type system extensions like a 4 Tesla magnet attracts iron nails... And most of these extensions seem to serve no useful purpose, as far as I can determine. And yet, all nontrivial Haskell programs *require* the use of at least 3 language extensions. It's as if everyone thinks that Haskell 98 sucks so much that it can't be used for any useful programs. This makes me very sad. I think
Which ones? The only one that comes to mind is hierarchical libraries, which are a Good Thing --- the H98 flat namespace becomes increasingly restrictive as Haskell gains more libraries (both included ones, and from e.g. Hackage.) Keep in mind also that many of these extensions are part of Haskell Prime, which last I checked is supposed to become official sometime later this year.
Haskell 98 is a wonderful language, and it's the language I use for almost all my stuff. I don't understand why people keep trying to take this small, simple, clean, elegant language and bolt huge, highly complex and mostly incomprehensible type system extensions onto it...
Experimentation. There are things you can't do with straight Haskell 98 (even something as simple as the State monad benefits from functional dependencies; but fundeps are troublesome enough that associated types are being explored as a cleaner alternative). Haskell's in kind of a strange position, being simultaneously a research language and a language which is useful in the "real world". The tension between these is one reason why there are standards (H98 and the upcoming H'): we "real world" types write to H98 or H' (increasingly the latter), while the researchers play with type system extensions and the like. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH