Hi! I have a question about guarantees that GHC provides about shape of generic representation of data type. To be more concrete if we have two single-constructor data types with N fields will their binary trees built from (:*:) be balanced in same way? Same for (:+:) binary tree. I want to use generics to write conversions between data types with same shape:
λ> data Foo = Foo Int Char deriving (Show,Generic) λ> to . coerce . from $ Foo 1 'c' :: (Int,Char) (1,'c') λ> to . coerce . from $ Foo 1 'c' :: (Sum Int,Char) (Sum {getSum = 1},'c') λ> to . coerce . from $ (Sum (1::Int), 'c') :: Foo Foo 1 'c'
Coercion between Reps for different types is only possible when they have same shape. Quick experiments shows that they're same. I think that they should be same but documentation is silent about this. Thanks in advance, Alexey