This sounds rather similar to C++'s constexpr functions and I would totally be in favour for that sort of thing, but I figured that reusing Typed TH would be a less cumbersome way to implement this. If people are in favour of a more elaborate approach, I'm all ears, but I fear that might be out of my league to implement :)
Cheers, Merijn > On 6 Feb 2015, at 21:54, Gershom B <gersh...@gmail.com> wrote: > > I recall having some discussions with Mathieu Boespflug regarding how the > static pointers work could be of use here. (And also Richard Eisenberg?) In > particular, we want to demand a special property of our validation functions > -- that they can safely be used at compile-time without necessarily "linking > in the world" and invoking the whole of template haskell. > > A function that is "static" should in a sense have this sort of property? And > so requiring that our validation functions be static seems like a useful > thing from an implementation standpoint. Static semantics might also help > "force the thunk" on what the correct relationship to polymorphism is. > > I guess the remaining question is then where to add them. I suppose we could > stick them with special semantics on Num and IsString or the like and do it > by magic? > > Alternately we could maybe have a whole class of "compile-time static > functions" that we just explicitly use, and all have the property that they > have type "a -> a" for some concrete "a", and that the value they are applied > to is static. These functions are then applied at compile time, and forced to > whnf. If they toss an error it is a compile error, otherwise they are not > present in the generated code. > > There are other design variations possible, but that one feels pretty neat to > me, if feasible. > > So then I could write > > foo :: Even > foo = even 6 > > for example, and get errors at compile-time. > > On top of this we could add a special way to augment Num, IsString, etc with > such methods to yield the desired: > > foo :: Even > foo = 6 > > -gershom > _______________________________________________ > ghc-devs mailing list > ghc-devs@haskell.org > http://www.haskell.org/mailman/listinfo/ghc-devs
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