Can branch-pattern be supported?

[JackSho]

Problem

In Clojure maps, distribution is often based on the value of a field (e.g., type). When the value changes, the key in the map also changes.

When I pull, I need to specify all possible keys, as I don't know the value of :type.

;; Type :a has keys qualified with ns a, and similarly for type B.
((query '{:type ?type
          :a/k1 ?a-k1
          :a/k2 ?a-k2
          :b/k1 ?b-k1 ;; keys of B must be written when pull
          })
 {:type :a
  :a/k1 1
  :a/k2 2})
;;=>
{?type :a
 ?a-k1 1
 ?a-k2 2
 ?b-k1 nil ;; confused.
 &?    {:type :a
        :a/k1 1
        :a/k2 2}}

Suggestion

Is it possible to provide a branching design that ensures a one-to-one correspondence between the pattern and the actual data?

[JackSho]

First idea. use case like in clojure.core, need to merge the case result-expr. if :type = :a, merge result is {:type ?type :a/k1 ?a-k1 :a/k2 ?a-k2}.

case is just an example, it can be other symbol in clojure.core such as if, when, and so on.

((query '{:type (case ?type
                  :a {:a/k1 ?a-k1 :a/k2 ?a-k2}
                  :b {:b/k1 ?b-k1 :b/k2 ?b-k2})
          })
 {:type :a
  :a/k1 1
  :a/k2 2})
;;=>
{?type :a
 ?a-k1 1
 ?a-k2 2
 &?    {:type :a
        :a/k1 1
        :a/k2 2}}