How to have variable to hold value to be updated imperatively? I need to have a variable to hold the value of a map that may need to be updated from time to time and globally accessed by functions for computation. What is the proper way to achieve that? While it works with the following code:

(with-local-vars [database {}]
  (var-set database (assoc @database :a 1))
  @database)

(with-local-vars [database {}]
  (let [lines ["* " "Something else"]]
    (for [line lines]
      (if (re-seq #"^*\s+" line)
        (do
          (var-set database (assoc @database :a 1))
          line)
        line))
    )
  )

1. Caused by java.lang.ClassCastException
   class clojure.lang.Var$Unbound cannot be cast to class
   clojure.lang.Associative (clojure.lang.Var$Unbound and
   clojure.lang.Associative are in unnamed module of loader 'app')

                   RT.java:  827  clojure.lang.RT/assoc
                  core.clj:  193  clojure.core/assoc
                  core.clj:  192  clojure.core/assoc
                      REPL:  193  yubrshen.enigma-clj/eval13051/iter/fn/fn
                      REPL:  190  yubrshen.enigma-clj/eval13051/iter/fn
              LazySeq.java:   42  clojure.lang.LazySeq/sval
              LazySeq.java:   51  clojure.lang.LazySeq/seq
                   RT.java:  535  clojure.lang.RT/seq
                  core.clj:  139  clojure.core/seq
            core_print.clj:   53  clojure.core/print-sequential
            core_print.clj:  174  clojure.core/fn
            core_print.clj:  174  clojure.core/fn
              MultiFn.java:  234  clojure.lang.MultiFn/invoke
                pprint.clj:   40  cider.nrepl.pprint/pr/fn
                  AFn.java:  152  clojure.lang.AFn/applyToHelper
                  AFn.java:  144  clojure.lang.AFn/applyTo
                  core.clj:  667  clojure.core/apply
                  core.clj: 1977  clojure.core/with-bindings*

Hi. How to simplify the following code?

(defn data-changed? [data new-data]
  (or (not= (:a data) (:a new-data))
      (not= (:b data) (:b new-data))
      (not= (:c data) (:c new-data))))

Isn't that just not=

select-keys with a not=

There could be more than just those three keys

Ahh, got it. Thanks.🙂

Again a day where Clojure makes me feel stupid. I can't find the error in a very basic function. (You could test this phenomena yourself via the code snippet at the very end.) The fn is just transforming a vector of maps into a map according to the map values. For instance, [{:id "aaaa" :c "cccc" :d "ddddd"} {:id "bbbb" :c "xxxx" :d "something else"}] is supposed to lead to {"aaaa" {"cccc" {:id "aaaa" :c "cccc" :d "ddddd"}}, "bbbb" {"xxxx" { {:id "bbbb" :c "xxxx" :d "something else"}} when called with :id :c as args. Here is the function that should do the job but doesn't: (defn vec-to-map-2 [vec-of-maps kw & kws] (let [kws-vec (vec (conj kws kw)) log (println (str "kws: " kws-vec))] (loop [vec vec-of-maps map {}] (if (empty? vec) map (let [first-map (first vec) check-1 (print (str "map: " first-map)) check-2 (print (str "a-kws: " kws-vec)) index-path (map (fn [x] (get first-map x)) kws-vec) check-3 (println (str "index-path: " index-path)) ext-map (assoc-in map index-path first-map) check-4 (println (str "ext-map: " ext-map))] (recur (rest vec) ext-map)))))) (5 Lines are just logging to find my mistake.) Error is: Instead of taking/getting the map's values the fn uses the map's keys:

kws: ["table_name" "column_name"]

map: {"ordinal_position" 14, "is_identity" "NO", .... ABBREVIATED  "table_name" "spiel", "numeric_precision_radix" nil, "generation_expression" nil, "data_type" "boolean", "column_name" "spielleitung", .... ABBREVIATED}
a-kws: ["table_name" "column_name"]
index-path: ["table_name" "column_name"]

ext-map: {"table_name" {"column_name" {"ordinal_position" 14, "is_identity" "NO", "character_set_name" nil, "scope_schema" nil, "character_octet_length" nil, "table_name" "spiel", "numeric_precision_radix" nil, "generation_expression" nil, "data_type" "boolean", "column_name" "spielleitung", .... ABBREVIATED}}}

map: {"ordinal_position" 14, "is_identity" "NO", "character_set_name" nil, "scope_schema" nil, "character_octet_length" nil, "table_name" "spiel", "numeric_precision_radix" nil, "generation_expression" nil, "data_type" "boolean", "column_name" "spielleitung", .... ABBREVIATED}

kws-vec: ["table_name" "column_name"]

index-path: ("spiel" "spielleitung")

ext-map: {"spiel" {"spielleitung" {"ordinal_position" 14, "is_identity" "NO", "character_set_name" nil, "scope_schema" nil, "character_octet_length" nil, "table_name" "spiel", "numeric_precision_radix" nil, "generation_expression" nil, "data_type" "boolean", "column_name" "spielleitung", .... ABBREVIATED}}}

can you someone explain simply how with-redefs is different from let?

Hi friends. Looking for a concise way to: • declare tests • short circuit on the first non-nil test • thread off of the test's value • stay out of macro-land What I'd like:

(what-i-want-> {:a 1 :b 2}
  :c dont-do-this
  :b print
  :a dont-because-already-short-circuited) ;; 2

(let [{a :a b :b c :c} {:a 1 :b 2}]
  (cond
    c (dont-do-this c)
    b (print b)
    a (dont-because-already-short-circuited a))) ;; 2

Is there a core higher order fn than only applies f if its arg x is not nil? Similar to fnil, but avoids calling f at all if x is nil. Something like this:

(defn fwhen
  [f]
  (fn [x]
    (when x
      (f x))))

#(some-> % f)