apfelmus wrote:
Andrew Coppin wrote:
OOC, can anybody tell me what ∀ actually means anyway?
http://en.wikipedia.org/wiki/Universal_quantification http://en.wikipedia.org/wiki/System_F
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.)
I do recall that GHC has some weird extension called "existential quantification"
http://haskell.org/haskellwiki/Existential_types http://en.wikibooks.org/wiki/Haskell/Existentially_quantified_types
Erm... oh...kay... That kind of makes *slightly* more sense now... 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 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...