Language Tour Question

[wintry knot]

I'm going through the Gleam Language Tour and noticed something that confused me.
On the https://tour.gleam.run/standard-library/list-module/ page there is an example for fold that goes as follows: io.debug(list.fold(ints, 0, fn(count, e) { count + e }))
Shouldn't that be: io.debug(list.fold(ints, 0, fn(e, count) { count + e })) because ints maps to iterating over e and count is the running total? The result is the same in this case, but might not always be?

[solemn cave]

Gleam is a data-first language

It means you can do this

list.fold(items, set.new(), set.insert)

[slate blaze]

https://hexdocs.pm/gleam_stdlib/gleam/list.html#fold
That's why the callback you pass to fold takes the accumulator as its first argument

[wintry knot]

Right, so because pipelines and such (data-first) it's just flipped, so it reads as "For each item in this list, starting at X do Y" but in actuality it runs as "Starting at X, for each item in this list do Y"

[solemn cave]

I don't know what you mean, sorry

[wintry knot]

You pass in 3 arguments into fold(), the list (aka "for each item in this list" in my previous message), the starting point/initial (aka "X" in my previous message) and the function (aka "Y" in my previous message). So you say list.fold(list[1, 2], X, Y(X, List[1, 2])) which then runs Y(Y(X, 1), 2). So although your first parameter for calling list.fold() is list[1, 2], in this case, it's passed in as the second parameter into Y (and the same for X being passed in as the second argument to list.fold() but is the first parameter when it's passed into fn Y(). Does that make any sense? 😄

I feel like I'm basically rewriting the docs that Jak posted, but in a confusing manner

  over list: List(a),
  from initial: b,
  with fun: fn(b, a) -> b,
) -> b``` 
All I'm trying to confirm is that although you pass in `List(a)` __first __into `list.fold()` , it's being used as the __second __ parameter for the function you're folding with.

Therefore io.debug(list.fold(ints, 0, fn(count, e) { count + e })) is correct because ints is being mapped to e and 0 is being mapped to count

[solemn cave]

Aye, because the data goes first

The data of list.fold is the list

the data of the reducer is the accumulator

They have different subjects

This is consistent throughout the Gleam ecosystem

[wintry knot]

✅

Thanks for your time and help 🙂

[solemn cave]

thank you thank you

[wintry knot]

Do I have to mark it as solved or.. ?