Hi Adam, > On 9 Feb 2015, at 17:44, Adam Gundry <[email protected]> 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
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