[Haskell-cafe] If you'd design a Haskell-like language, what would you do different?

[Conor McBride]

On 22 Dec 2011, at 17:49, Bardur Arantsson wrote:

> Alexander Solla wrote:
>
>> I happen to only write Haskell programs that terminate.  It is not  
>> that
>> hard.  We must merely restrict ourselves to the total fragment of the
>> language, and there are straight-forward methods to do so.
>
> Do (web/XML-RPC/whatever) server type programs terminate?

No, but "total" and "terminating" are not the same. Those *co*programs
will, if they're any good, be total by virtue of their productivity
rather than their termination.

What's slightly controversial is the claim that we "must merely restrict
ourselves to the total fragment of the language". It would be more
controversial to claim that some new Haskell-like language should
restrict us to total programs. I'd be glad if "pure" meant "total", but
partiality were an effect supported by the run-time system. Then we
could choose to restrict ourselves, but we wouldn't be restricted by the
language.

This is not the first time the issue has surfaced, nor will it be the
last. It's customary at this point to object that one wouldn't want to
program with the monadic notation, just for the effect of partiality.
I'd counter that I don't want to program with the monadic notation,
for any effects: I'd like to program with an applicative notion, but
in monadic types. That's what I'd do different, and for me, the subject
is not a hypothetical question.

All the best

Conor