Hi Nickolay,
I'm not sure why your version was *that* slow. But the algorithm was not
optimal. I translated the Haskell Report prelude version of nub to the type
level. That version compiles instantly with the long list. I tested with
GHC 7.10.2.
https://gist.github.com/roelvandijk/f115c6b85a3961e1b689
Regards,
Roel
2016-02-07 14:37 GMT+01:00 Nickolay Kudasov
Dear Cafe,
I have faced a type-level performance problem (with GHC 7.10.3). I am trying to implement type-level Nub which removes duplicates from a type-level list.
My implementation [1] with an example of a list of length 20 takes forever to compile. If you reduce the size of the example list (e.g. to 15 items), it will compile faster. Also, if you remove the Nub application from exampleVals, it compiles instantly (this is how I know the problem is in Nub).
My question is how can I speed up type-level Nub? And less importantly why exactly is it this slow?
The practical application for this is building automatic tests [2] for servant-swagger. There I am interested in generating exactly one test for each distinct type.
Kind regards, Nick
[1] https://gist.github.com/fizruk/06458fe8b62a1e562af1 [2] http://hackage.haskell.org/package/servant-swagger-1.0.2/docs/Servant-Swagge...