[Exercism] what `treasure` is doing here?

[zealous flax]

this is related to the treasure challenge on exercism:
https://exercism.org/tracks/gleam/exercises/treasure-chest/edit

and there is this part of the code:

pub fn get_treasure(
  chest: TreasureChest(treasure),  
  password: String) 
  -> UnlockResult(treasure) {  
}

i'm not sure what treasure in chest: TreasureChest(treasure) is doing. Maybe is a generic, but then i'm not sure where is coming from. I feel like i'm having a misunderstanding of how things work here

[deft knot]

That's right, TreasureChest and UnlockResult are generic types

The intro for that exercise explains what generics are https://exercism.org/tracks/gleam/exercises/treasure-chest

[zealous flax]

yes, i've done that. and I know what generics are and generally how to use them. i'm specifically confused about what treasure is doing. it seems to me that is some kind of destructuring?! i'm really not sure

[deft knot]

It's just normal generics

In Gleam it's () rather than the <> you'd find in languages like Java

Otherwise it is largely the same

[zealous flax]

so treasure is the generic type that is on that treasure chest "instance"?!

[deft knot]

pub fn get_treasure(
  chest: TreasureChest(treasure),  
  password: String) 
  -> UnlockResult(treasure) {  
}

In TypeScript syntax it would be this

export function getTreasure<Treasure>(
  chest: TreasureChest<Treasure>,
  password: String,
): UnlockResult<Treasure> {
}

treasure is a type variable, so the get_treasure function works with TreasureChest types of any type as their parameter

[zealous flax]

ic. thx. the () is what confused me. to me, it looked like it was destructuring.

is there anywhere where I can read about the reason why using () instead of <>? I feel like using <> would make easier to read and allow a shorthand for types variants that have the same name to be written easier. something like how Kotlin does:

pub type Cat(name: String)

instead of

pub type Cat {
  Cat(name: String)
}

but I don't know the reason why the other way, so i'm curious

[deft knot]

The reason is to make the language simpler

No reason to have a different syntax for calling type constructors and value constructors

A constructor is a constructor, and there's only one syntax for it

No particular reason to copy Java, other than being more familiar to folks coming from Java inspired languages