Release plans

Simon Peyton-Jones simonpj at
Tue Apr 17 10:02:15 EDT 2007

| Yes, but where is it written that what cannot be expressed in system-
| F is type incorrect? We think it is still type safe, and it is an
| extrcat of a larger program that is quite useful (if we managed to
| compile it),

Indeed!   Well-typed programs don't go wrong, but not every program that never goes wrong is well-typed.  It's easy to exhibit programs that don't go wrong but are ill-typed in System F, or indeed any other decidable type system.  Many such programs are useful, which is why dynamically-typed languages like Erlang and Lisp are justly popular.

However, I think EHC is still in the statically-typed camp.  In which case, if EHC accepts the program you sent then presumably EHC implements a type system in which the program is well-typed.  What is that type system?   I hazard that it is even more exotic than GHC's!  And probably very interesting as well; I'd love to see it.

I'm quite puzzled about why Hugs accepts it though. I don't think Hugs has ambitions to be more expressive than System F.

(Incidentally, GHC is indeed going beyond System F -- we've recently changed GHC to use FC as its intermediate language -- paper on my home page.  But even FC can't express your program.)


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