alt Hacker NewsMap and filter usually have only one arg and if they have 2, the 2nd is almost always a 0-based index. They look identical in most languages, even when Microsoft chooses to call them Select and Where.
Reduce has an accumulator and a 2-arg function and languages are not very consistent amongst each other as to whether it's reduce(initial_acc, callback(acc, elem)) or reduce(callback(acc, elem), initial_acc) or reduce(callback(elem, acc), initial_acc) or what.
Hard to remember. Also some languages have a version of reduce that doesn't take an initial accumulator at all, which is just a footgun waiting for you to hit an empty collection. Also ALSO, the accumulator can easily become awkward in languages that don't support anonymous types or don't support easy mutation of an anonymous type record. Which is most of them!
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In GNU Guile `reduce` is described as a special case of `fold`, where the first element is suitable to be used as initial value, while `fold` is more general and lets you specify another initial value. I think that makes a lot of sense.
Also reduce is a weird name.
> … to call them Select and Where.
While map is a great name, I always struggle to remember if ‘filter’ keeps elements that match the condition or removes them.
I mean, it’s like a colander: you filter noodles and water, but which one do you keep? The noodles, right? But, replace noodles with tea and now you want to keep the water part.
Naming is hard I guess.
It doesn't help that fold/reduce often have different orders depending on the ecosystem. Every few months when I have a reason to reach for `fold` in nutshell I forget that it has the next element as the first arg instead of the second, which is what I'm used to from Rust. I guess I should just be happy I don't need to specify which direction I want like in OCaml.