DeriveFoldable treatment of tuples is surprising

[Twan van Laarhoven]

On 2017-03-21 21:34, David Feuer wrote:
> This seems much too weird:
>
> *> :set -XDeriveFoldable
> *> data Foo a = Foo ((a,a),a) deriving Foldable
> *> length ((1,1),1)
> 1
> *> length $ Foo ((1,1),1)
> 3

This is not unique to tuples, consider:

     > :set -XDeriveFoldable
     > data Foo a = Foo [[a]] deriving Foldable
     > length [[1,2]]
     1
     > length $ Foo [[1,2]]
     2


Twan