Add support for function schema

[Jimdooz]

Hi,

I've been exploring the current features and noticed that function schema validation, similar to what's available in Zod, isn't part of the project. I think incorporating this could enhance the functionality for users who rely on strict typing for functions.

I was thinking about something like this

const MyFunctionSchema = v.function()
  .args(
    v.string()
  )
  .returns(
    v.boolean()
  )

type FunctionSchema = Output<typeof MyFunctionSchema >;

[fabian-hiller]

Thank your for creating this issue. In Valibot we don't chain methods. Instead it will probably look something like this:

const MyFunctionSchema = v.function([v.string()], v.boolean());

What is your use case for a function schema? I haven't figured that out yet. That's why it's not part of the library. But I am happy to add it.

[Jimdooz]

Thank you for your reply!

Yes, you're right, this declaration format will be more in line with current syntax.

My use case involves a list of validators where each has a name and a corresponding validation function. I'm aiming to automate the process of checking argument schemas against these validators. Having function schema validation would streamline this process, ensuring that each function receives the correct type and structure of data before processing.

[fabian-hiller]

Thank you for your reply. Can you imagine creating a PR with a function_ schema function? The code does not have to be perfect. Valibot is implemented very simply. You can copy the basic structure from another schema.

[Jimdooz]

Yes I can try :)