It is common to say "Foo implements the Fooer interface" in the doc on the function. Also, looking up what interfaces a type implements is 1.) impossible (depends on what other interfaces exist in the universe), 2.) pointless - you shouldn't care what interfaces it implements, you should look for functions that you want to use with your type.
You're also missing one of the best parts of implicit interfaces - you can use other people's types in your own functions with interfaces that didn't even exist when they wrote their type. To do that in languages with explicit interfaces, you have to write ugly wrapper classes around the other person's type for zero benefit.
Haskell typeclasses are an interesting way to achieve the same effect explicitly - if your module implements/returns/requires some type, then I can make your type "be" a member of my typeclass (pretty much equivalent of your class implementing my interface) without touching your module or creating a new type; the explicit declaration can be made afterwards to join together two modules that didn't know that the other existed but have types that are similar enough.
Only if the type already defines the methods for that interface. In e.g. Rust you can define whatever interface (trait) you want for external types. No need for wrappers.
Ahh, that's cool, I didn't realize Rust could do that.
Though it does still require you to write the thing that tells the compiler their type implements your interface, right? Not a huge deal, but it's still essentially like writing a wrapper (though perhaps not as huge?)
Also, it sounds like you can't implement a third party trait on a third party type, so you can't use bill's cool log writer in joe's cool log roller.
You're also missing one of the best parts of implicit interfaces - you can use other people's types in your own functions with interfaces that didn't even exist when they wrote their type. To do that in languages with explicit interfaces, you have to write ugly wrapper classes around the other person's type for zero benefit.