Simplify Reporter type

[OliverJAsh]

The docs state a Reporter type as:

interface Reporter<A> {
  report: (validation: Validation<any>) => A;
}

However, it could just be a function instead:

(validation: Validation<any>) => A

This is a nitpick, but I noticed I accidentally deviated from your standard in my library, https://github.com/OliverJAsh/io-ts-reporters, where I just export a reporter function.

Does it make sense to simplify the type here, or are there reasons for keeping it as a function on an object?

[gcanti]

are there reasons for keeping it as a function on an object?

For consistency. It's just how type classes are encoded in fp-ts (static dictionaries)