Using `juxt` to compose and apply multiple validation functions against the same value

juxt_validate.clj

(ns juxt-validate
  (:require [clojure.string :as string]))

(defn validate-format
  [v]
  (if (every? #(contains? v %) #{:name :email :id})
    [:ok v]
    [:error {:invalid-format "expected id, name, and email"}]))

(defn validate-email
  [v]
  (if (some-> v :email (string/includes? "@"))
    [:ok v]
    [:error {:invalid-email "email is invalid"}]))

(defn validate-name
  [v]
  (if-not (some->> v :name str (re-find #"\d+"))
    [:ok v]
    [:error {:invalid-name "names cannot contain numbers"}]))

(defn collect-validation-results
  [{error-merge-fn :error-merge-fn
    :or {error-merge-fn identity}}
   validators
   value]
  (let [r ((apply juxt validators) value)
        {ok :ok
         err :error} (group-by first r)]
    (if (seq err)
      [:error (error-merge-fn (map second err))]
      [:ok (last (last ok))])))

(defn merge-tagged-map-errors
  [errs]
  (let [merge-maps (fn [x y] (merge-with #(conj (if (coll? %1) %1 [%1]) %2) x y))]
    (reduce
     merge-maps
     errs)))

(defn validate-request
  [r]
  (collect-validation-results
   {:error-merge-fn merge-tagged-map-errors}
   [validate-format
    validate-email
    validate-name]
   r))

(comment
  (validate-request {}) ;=> [:error {:invalid-format "…", :invald-email "…"}]
  (validate-request {:email "a" :name 1}) ;=> [:error {:invalid-format "…", :invald-email "…", :invalid-name "…"}]
  (validate-request {:id 1 :email "a@b.com" :name "A B"}) ;=> [:ok {:id 1 :email "a@b.com" :name "A B"}]
  :rcf)