Correction about the latter part...
> In the end, I would write something like the following: > > unGen arbitrary (mkStdGen 11) 5 :: [Int] >> > > This produces, for example, [5,1,-2,-4,2]. I also want to generate the same > value for a type isomorphic to [Int]. > > unGen arbitrary (mkStdGen 11) 5 :: List Int >> > > Unfortunately, this produces Cons 4 (Cons 3 (Cons (-2) (Cons 0 (Cons (-1) > Nil)))): same length but different values. The Arbitrary instances are the > same. The Arbitrary instance were _slightly_ different, but different enough. ;) Now, the values are isomorphic. Thankfully, purity is restored. Sean
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