[Haskell-beginners] Foldable for (,)
voldermort at hotmail.com
Sun Apr 23 10:06:00 UTC 2017
If a tuple only has one value, why do functions for operating over sets make sense at all? I can see from your explanations why the answers could be considered correct (if a particular convention is assumed), but why does the operation make sense at all? It seems like we're asking for the length of a single value, its product, etc.
Francesco Ariis 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?
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:
| +------------- I am the value
+--------------- I am an annotation (and since tuples arguments can
be heterogeneous, I could be a String, a Bool,
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?
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