On Sun, Apr 23, 2017 at 08:21:34AM +0000, Jonathon Delgado wrote:
I've seen many threads, including the one going on now, about why we need to have:
length (2,3) = 1 product (2,3) = 3 sum (2,3) = 3 or (True,False) = False
but the justifications all go over my head. Is there a beginner-friendly explanation for why such seemingly unintuitive operations should be allowed by default?
Hello Jonathon, the proponents of `Foldable (a,)` see `(2,3)` not as a pair of 'equal' values, but as a value *and* an annotation, much like some other folks see Either as having a value (Right a) *or* an annotation (usually an error in the form of Left e). So to go back to your examples: (2,3) ^ ^ | +------------- I am the value | +--------------- I am an annotation (and since tuples arguments can be heterogeneous, I could be a String, a Bool, anything). If you agree with this paradigm, `length`, `sum` and friend become a bit less icky. I would prefer tuples to be unbiased, but this intuition helped me connect with the people on the other side of the line. Does this help?