On Tue, Apr 24, 2012 at 9:26 AM, Yitzchak Gale
Greg Weber wrote:
I very much agree with you. However, when we complain about something essentially we are asking others to prioritize it ahead of other things. I don't think any more visibility of this issue is going to improve its prioritization. I suspect your only way forward right now is to start implementing something yourself.
You're right. But as a professional Haskell developer, I am under the same kinds of deadline pressures as any other professional. So I'm afraid it's not going to be me, at least not in the near future.
However, what I can do is raise the red flag. Some people are pushing things in directions which would cause OverloadStrings to become more and more ubiquitous, perhaps even the default. I want to make sure that the people who are doing that are aware of the deep problems with that approach.
Sure, as much as anyone else, I want string literals that can be typed as Text. But not at the cost of delaying syntax checking to run time.
And, as Bas points out, that there are many different compile time mechanisms that could be used for this.
Thanks, Yitz
Here's a theoretically simple solution to the problem. How about adding a new method to the IsString typeclass: isValidString :: String -> Bool We can give it a default implementation of `const True` for backwards compatibility. Then, whenever GHC applies OverloadedStrings in a case where the type is fully known at compile time (likely the most common case), it can run the check and- if it returns False- stop the compile. This has the benefits of letting existing code continue to work unchanged, and not requiring any Template Haskell to be involved. A downside is that it will still let invalid code through sometimes. Perhaps a solution is to modified the OverloadedStrings extension that requires that the type be fully known. If someone *really* wants polymorphic strings, they can explicitly add `fromString`. I actually think I'd prefer this version. Michael