Type an array

[theogiraudet]

Hi!

First of all, thank you very much for this nice library, my type validation rules in Langium were starting to get a bit messy and I think I can replace some of them thanks to this library. :D
I'm not really familiar with type system design so maybe my question is a bit naive.
With the current state of Typir, is it possible to define typed arrays?
In my language, I have something like that:

entity Foo {
  prop bar: unique integer[0..3] = [1, 2, 3]
}

And I want to:

• Check if the value is an array of integer
• Check if the size of the array is between 0 and 3
• Check if each element of the array is unique (no duplicates)

I don't know if the two last rules are in the scope of a type system, but concerning the first, I would like a generic method to not have to declare a rule for each of my types.
Currently, in my language I have:

• Primitive types: boolean, integer, float, string
• Entity types
• Enumeration types

So the two lasts are types defined by the user.

This question may be linked to #34.

Thanks!

[JohannesMeierSE]

Hello @theogiraudet,

thanks for your interest in Typir!

With the current state of Typir, is it possible to define typed arrays?

Officially not yet, but we are working on types we are calling FixedParameterType at the moment. They are designed to represent types like Set<A>, Collection<B> or Map<K, V>, or in your case Array<Integer>. First implementations are already on main and here is a sketch how to use them. But there are no test cases for them, support for cyclic type definitions is missing and so on. We plan to support this feature for v0.2 (#44)

Check if the value is an array of integer

Yes, type inference will be supported for this case

Check if the size of the array is between 0 and 3

The number of elements inside an array variable at runtime is not part of a type system. But "restricting" an unlimited array (or list) with a size (or upper limit, which is constant and independent from the actual number of elements in the array at runtime) is another, cross-cutting feature. It is not under develop right at the moment, but on our roadmap: #38 describes it for primitive types, but such restrictions will very likely be supported for any types.

Check if each element of the array is unique (no duplicates)

No, such a check is not part of Typir, since it is not enough, that the elements have the wanted type (that is a type-related validation yes), but all their values/properties need to be the same (which is a "usual" validation beyond type checking).

Primitive types: boolean, integer, float, string

Yes, they are already supported by Typir

Entity types

We support nominally typed classes at the moment. Maybe you can reuse them for your DSL and just don't specify any methods.

Enumeration types

They are on our roadmap, I just created #61 to make that explicit 🙂

types defined by the user

That is supported by Typir and demonstrated in this example with user-defined functions and classes. Additionally, this example has some fixed primitives.

This question may be linked to #34

That depends on your DSL, in particular its operators (and predefined functions?). In the examples you showed above, I saw no "dynamically computed types".
But if you want to support something like the following example, you will need this feature:

entity Foo {
  prop bar1: unique integer[0..2]
  prop bar2: unique integer[0..3]
  prop bar3: unique integer[0..4] = bar1 + bar2 // If "+" represents array concatenation,
    // you might want to have a type-related validation here,
    // since the resulting array might have 3+4=7 elements, but bar3 stores only 5 elements.
}

my type validation rules in Langium were starting to get a bit messy and I think I can replace some of them thanks to this library

We looking forward to hear about your experience and get some feedback to improve Typir!

[theogiraudet]

Thank you very much for your detailed answer!
I will look at the unofficial version until it is brought into the official API.
Can't wait to see what we can do with Typir in the future, I'll be following the project closely!