4 ms·

I agree, and not just the English. There is use of particular notation that does not explain anything unless you already know what it means: > f is a morphism

I agree, and not just the English. There is use of particular notation that does not explain anything unless you already know what it means: > f is a morphism from a -> b, and g is a morphism from b -> c; g(f(x)) must be equivalent to (g • f)(x) If I don't already understand (g • f)(x) this is not helpful at all. This other one especially jumped out at me (perhaps because I've personally never seen this "bent equals sign" ≍ before): > A functor must adhere to two rules: > Preserves identity > object.map(x => x) ≍ object What does that sign ≍ mean? If I don't know, I am no closer to understanding functors. And the sign is not explained anywhere in the document.

cratermoon 4y ago
Oh boy. I didn't put on my glasses to read it so I didn't notice that ≍ is not = and that's important. I think in the context it just means the result is in the range of "function applied to object"
hither_shores 4y ago
> What does that sign ≍ mean? Normally, `f ≍ g` means `f \in \Theta(g)`. Here, the author is using it as an equals sign. I have no idea why.
- cratermoon 4y ago
  Except it's not and =, it's a ≍ sign, which looks almost identical. I'm not a mathematician and I don't know the deep theory behind functional programming, but the internet tells me that ≍ in Graham, Knuth, and Patashnik's Concrete Mathematics it's defined to mean the same thing as "Big Θ"[1], as you note. 1 https://math.stackexchange.com/questions/764897/what-does-this-asymp-symbol-mean-subject-analytic-number-theory https://math.stackexchange.com/questions/764897/what-does-th...