Re: Proposal: ValidateMonoLiterals - Initial bikeshed discussion

Hi Adam,

On 9 Feb 2015, at 17:44, Adam Gundry wrote: In the absence of a coherent story for polymorphism, I think the right thing to do is to be able to specify a particular validator, rather than try to have type inference determine a monomorphic type and otherwise get stuck...

I was planning to write a TH library for this sort of thing anyway, I was just curious if people had better solutions for the polymorphic story/solutions to take away this annoyance. But maybe a better solution in this direction is Gershom's solution to allow proper compile time functions.

...so is the right solution to introduce Typed TH quasiquoters for expressions? Sorry, I presumed such a thing existed, as Typed TH is rather regrettably underdocumented. Is there any particular difficulty with them, or is it just a Small Matter of Programming?

I don't actually know the answer to this, it was one of the questions I was hoping to answer in this discussion :)

I think the lack of Lift instances is a separate problem; while it looks like 7.10 will be better in this respect and dataToExpQ goes a fair way, I agree that making them easier to generate would be nice. Perhaps a generics-based default method combined with DeriveAnyClass would make "deriving Lift" possible?

It's not directly related to whatever solution we pick, but I do think it's an important issue. There's currently a TH library for deriving them, but from what I've seen about writing them by hand I don't understand how GHC couldn't trivially generate them for most (all?) ADTs. Cheers, Merijn