Call to clojure.core/fn did not conform to spec

Question

This question already has answers here: question from:https://stackoverflow.com/questions/65650159/call-to-clojure-core-fn-did-not-conform-to-spec

Answer 1

The problem is the -> macro you are using which inserts the threading value in the first position, right after the fn symbol. So this:

(map #(-> % int
          (- 48)
          (fn [x] (* x x))))

becomes something like:

(map #(fn
        (- (int %) 48)
        [x]
        (* x x)))

That is obviously invalid because fn expects the first arg to be a vector of function parameters, which is what the error message is trying to say:

fails spec: :clojure.core.specs.alpha/arg-list at: [:args :bs :arity-1 :args] predicate: vector?