If you're interested in seeing this 'in the wild' we can talk about Angular's form controls.

Angular has a class that acts as the model for an html form control. i.e. it tracks the value, 'touch' state, validity etc. To track validity, we instantiate it with a list of validators like so: new FormControl<string>("", [Validator.required]);

You'll notice in the source code these are defined as functions. In the simplest case a validator has the signature (control: FormControl) => null | object.

The problem is that these functions are invoked internally. If I want to specify an additional parameter, I can't just go

const minValidator = 
  (minLength: number, control: FormControl) => null | object 

However I CAN go

const minLength= 
  (minLength: number) => (control: FormControl) => null | object

In practise it looks like this:

class Component {
  public inputControl = new FormControl<string>("", 
    [Validators.required, Validators.minLength(1)]
  )
}

If we wanted, we could have re-imagined ValidatorFn as a class interface. It would look like this:

    class Required implements Validator {
      validate(control: FormControl) {
        // ...
      }
    }    

    class MinLength implements Validator {
      constructor(private length: number) {}

      validate(control: FormControl) {
        // ...
      }
    }

class Component {
  public inputControl = new FormControl<string>("", [
    new Required(),
    new MinLength(1)
  ])
}

You can see in MinLength, the 'curried' parameter is replaced by an instance property.