alpha12 fails with "UnsupportedOperationException nth not supported on this type: PersistentArrayMap"

[ulsa]

The following works with alpha11, but not alpha12:

(require '[clojure.spec :as s])
(require '[clojure.future :refer :all])
(require '[clojure.spec.test :as stest])

(s/def ::n nat-int?)
=> :user/n

(s/fdef sample
        :args (s/cat :some-map (s/keys :req-un [::n])))
=> user/sample

(defn sample [some-map]
  some-map)

(stest/instrument 'user/sample)
=> [user/sample]

(sample {:n 6})
UnsupportedOperationException nth not supported on this type: PersistentArrayMap  clojure.lang.RT.nthFrom (RT.java:947)

With alpha11:

...
(sample {:n 6})
=> {:n 6}

[ulsa]

Just tested with Clojure 1.9-alpha12 and it works fine. So it seems to be something related to the backport.

[tonsky]

Looks like it was related to changes in clojure.core which I don’t port. In 1.9 it’s ok to destructure map as sequence, in 1.8 it is not:

(let [[x & xs] {:n 6}]) => java.lang.UnsupportedOperationException: nth not supported on this type: PersistentArrayMap