I’m going through hexdocs and learning the fundamentals. I am getting the opposite result of what I would expect and I wondered if someone had an idea of what is happening here? Enum.reduce(1..4, 0, &-/2) # Expected -10, but observed 2 My understanding is that &-/2 shorthand capture should be fn …

&-2/ is &1 - &2, not &2 - &1. In Elixir the accumulator is given as the second argument to reduce, as you have seen in your second example. You expect it to be fn elem, acc -> acc - elem end but as you can see you have flipped the order of arguments. If you pass fn elem, acc -> elem - acc end as &-…

I copy-pasted the wrong version. Let me simplify with iex: iex(1)> Enum.reduce(1..4, 0, &+/2) 10 iex(2)> Enum.reduce(1..4, 0, &-/2) 2 Shouldn’t the latter with &-/2 be -10?

Can you show step by step why you think it should be -10?

The accumulator is the 2nd arg. So you are doing Let f(x, y) = x - y f(4, f(3, f(2, f(1, 0)))) = 4 - (3 - (2 - (1 - 0))) = 4 - (3 - (2 - 1)) = 4 - (3 - 1) = 4 - 2 = 2

I wanted to add to this post, to highlight potential issues with LLMs. I’m not a big fan of blindly using LLMs, but if I come across something I haven’t seen or don’t understand, LLMs can be helpful to give verbose answers. Here, my initial thought was that if Enum.reduce(1..4, 0, &+/2) # = 10 then…

[image] Why Enum.reduce fun arguments are x, acc instead of acc, x? Questions / Help Good day everyone! I am using Enum.reduce/3 ( Enum — Elixir v1.9.0-rc.0 ) function quite often and I am regularly wondering why are the arguments for reducing function x, acc instead of acc…

In the end LLMs are still just big pattern detectors and reappliers. The fact that many programming languages use acc, item might be enough of a signal to drown the fact that elixir doesn’t order parameters on the reduce callback that way. I just tried this with claude: The first verbose form: Enu…

In this specific case, the problem is that Elixir (and Erlang) chose the opposite signature for the reducer function: Elixir / Erlang: (element, accumulator) -> accumulator Haskell / Clojure / JS: (accumulator, element) -> accumulator The explanation the LLM generates works for languages with the…

Just wanted to point out that the initial thinking of “if reducing with +/2 over some list produces n, -/2 will produce -n” is incorrect because of the properties of addition and subtraction. Addition is commutative and associative, and subtraction is not commutative (it’s anti-commutative) and not …

Enum.reduce with &-/2 produces unexpected results

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stefanluptak November 25, 2024, 8:55am 8