Clojurians Log v2

Hello Meanderites! Been banging my head against the wall for this one; let's say I wanted to replace all the keys' namespaces in a map with a given namespace, how could I go about doing that?

Total noob to Meander here.

Here's a contrived example. Say I have data shaped like this more or less:

{:foo 1
 :boo [{:abc true}]}

{:bar/foo 1
 :bar/boo [{:far/abc true}]}

And I'd like to have arbitrarily many keys at each level.

Hey @andre206 welcome 🙂 While there are definitely ways to solve your problem using meander, this is definitely not the sort of problem meander is focused on. Meander is focused more on concrete transformations and less on generic ones, that is one way it differs from things like specter. That said, by leveraging clojure’s facilities for dealing with arbitrarily nested things, we can definitely tackle this problem. First we can start with the non-nested case

(m/rewrite {:foo 1 :boo 3}
  (m/map-of (m/keyword !ks) !vs)
  (m/map-of (m/keyword "bar" !ks) !vs))

(require '[clojure.walk :as walk])

(walk/postwalk 
 (fn [x]
   (m/rewrite x
     (m/map-of (m/keyword !ks) !vs)
     (m/map-of (m/keyword "bar" !ks) !vs)
     
     ;; catch all for all non-map values
     ?x ?x))
 {:foo 1
  :boo [{:abc true}]})

Ah, many thanks! I think I understand Meander's purpose a bit more now

Glad that helped. I definitely should have mentioned the pure meander solution though.

(require '[meander.strategy.epsilon :as r])

((r/top-down
  (r/rewrite 
   (m/map-of (m/keyword !ks) !vs)
   (m/map-of (m/keyword "bar" !ks) !vs)
   ?x ?x))

 {:foo 1
  :boo [{:abc true}]})

Ah, that’s not too bad!

My problem, you see, is only partially generic. I’m trying to specify namespaces for nested entities (the namespace at each level of nesting is specific). I tried specter first then came upon Meander on HN. Specter’s API felt a bit clunky, and Meander’s logic style programming immediately appealed to me — but I realize my problem is not a perfect fit.

How do you know at what level of nesting you should use what namespace? Is there any predictability to the structure?

If you give your full real problem, there might be an good answer. Or at least I would know if there wasn’t.

Like for example, if there is some :type key that tells you the namespace and it was all just maps you could do something like this:

(def example 
  {:type "thing"
   :stuff {:type "stuff"
           :a 3
           :foo {:type "foo"
                 :c 5}}
   :b 3})

(m/rewrite example
  {:type ?type
   & (m/map-of (m/keyword !ks) !vs)}
  {:type ?type
   & (m/map-of (m/keyword ?type !ks) (m/cata !vs))}

  ?x ?x)