How do you compose two or more predicates in clojure?

If you want to compose them in an and relationship, use every-pred:

((every-pred pos? even?) 5)
;false
((every-pred pos? even?) 6)
;true
((every-pred pos? even?) -2)
;false

And if you want to compose them in an or relationship, use some-fn:

((some-fn pos? even?) 5)
;true
((some-fn pos? even?) 6)
;true
((some-fn pos? even?) -2)
;true
((some-fn pos? even?) -3)
;false

In Clojure 1.3 there is actually a built-in function called every-pred to do just this. See here.

(defn posint? [n]
  ((every-pred integer? pos?) n))

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