Protocols in cljs

[Pedro Viegas]

Hi! I am trying to annotate a protocol in clojurescript, but I am not being able to.

I am really lost.

(ns myproject.protocols

  (:refer-clojure :exclude [defprotocol])

  (:require [cljs.core.typed :as t :include-macros true]))

(t/defprotocol A

  (fmap [fv g :- (t/All [x y] (t/Fn [x -> y]))]

[fv g :- (t/All [x y] (t/Fn [x -> y])) fvs :- (t/NonEmptyColl A)]))

Can anyone help me?

Thx

[Ambrose Bonnaire-Sergeant]

I don't have time to check if this works in ClojureScript, but this equivalent should work in Clojure.

(defprotocol A

  ([a b] fmap

   [fv g :- [x -> y]] :- Result

   [fv g :- [x -> y] fvs :- (NonEmptyColl x)] :- Result))

[Pedro Viegas]

Thanks, probably I am requiring the wrong namespace, because I am getting:

Type Error (myproject.protocols:4:1) Found untyped var: cljs.core.typed/defprotocol

in: cljs.core.typed/defprotocol

[Ambrose Bonnaire-Sergeant]

Oh it's much more likely that defprotocol isn't implemented yet for ClojureScript. Hope to fix this soon.

[Pedro Viegas]

Oh, anyways, I saw that ann-protocol is there, but couldn't find any example using it with multiple arity, like my case.

Would it be possible to help me with an example?

[Ambrose Bonnaire-Sergeant]

Hopefully it's the same syntax as Clojure http://clojure.github.io/core.typed/#clojure.core.typed/ann-protocol

Could you explain the semantics of fmap?

Thanks,
Ambrose

[Pedro Viegas]

Sure, it should behave like a functor.

(ann-protocol Functor

  fmap

  (Fn [Functor [x -> y] -> Functor]

        [Functor [x -> y] (Coll Functor) -> Functor]))

This would be the behaviour on a string:

(defn fmap-string

  ([fv g] (apply str (g fv)))

  ([fv g fvs] (apply str (apply g fv fvs))))

(fmap #(apply str "A" %&) "b" "c" "d") => "Abcd"

[Ambrose Bonnaire-Sergeant]

It gets messier if you want to abstract over the Functor, but does this give you a start?

(ann-protocol Functor [[x :variance :covariant]]

  fmap

  (All [y]
   (Fn [(Functor x) [x -> y] -> (Functor y)]

         [(Functor x) [x -> y] (Coll (Functor y)) -> (Functor y)]))

[Pedro Viegas]

Yes it does! Thanks a lot for the quick reply.