Is there a Clojure compile-time tool to check if a record or type actually implements a protocol it claims to?

Question

Seems the Clojure compiler doesn't do this by default : Does the Clojure compiler check if records and types implement protocols?

Any, say, Lein plugins that do this?

Answer 1

The amazing core.typed introduces "an optional type system for Clojure", as you can see on their official website.

Specifically you may want to use their own defprotocol macro (from core.typed wiki) :

Protocol definitions should use clojure.core.typed/defprotocol whose syntax is reminiscent of defprotocol and typed fn:

(defprotocol IUnifyWithLVar
  (unify-with-lvar [v u :- LVar s :- ISubstitutions] :- (U ISubstitutions Fail)))

Polymorphic protocols are supported:

(defprotocol [a b] Lens
   (-fetch [l x :- a] :- b)
   (-putback [l x :- a v :- b] :- a))

Once installed, you run it via leiningen with lein typed check. The obvious downside is that you have to annotate your code. This is the cost to pay to increase the safety of your code by using static type checking.

You may also be interested by the functions satisfies?, and instance?.