On Tue, Sep 30, 2008 at 12:51 AM, apfelmus
Jason Dagit wrote:
Hello,
I recently had someone point me to this thread on LtU: http://lambda-the-ultimate.org/node/2003
The main paper in the article is this one:
http://www.jucs.org/jucs_10_7/total_functional_programming/jucs_10_07_0751_0...
It leaves me with several questions: 1) Are there are existing Haskell-ish implementations of the total functional paradigm?
Agda?
http://appserv.cs.chalmers.se/users/ulfn/wiki/agda.php?n=Main.HomePage
It seems to me that dependent types are best for ensuring totality.
Bear with me, as I know virtual nothing about dependent types yet. In the total functional paradigm the language lacks a value for bottom. This means general recursion is out and in the paper I cited it was replaced with structural recursion on the inputs. How do dependent types remove bottom from the language?
2) Could we restructure Haskell so that it comes in 3 layers, total functional core, lazy pure partial functional middle, and IO outer layer?
The IO layer can be interpreted as "co-total", i.e. as codata. Basically, this means that it's guaranteed that the program prints or reads something after a finite amount of time and does not loop forever without doing anything.
I was asserting that Haskell is currently 2 layered. Purely functional vs. IO. They integrate nicely and play well together, but I still think of them as distinct layers. Perhaps this is not fair or confusing though. The paper I cited did indeed use codata to define streams so that something, such as an OS, that needs to process infinite streams of requests can still do so. Thanks, Jason