Something like Clojure would be perfect for this. Write a macro that converts

    {"name" (includes? "k"), "age" (< 20)}

into

    {"name" #(includes? % "k"), "age" #(< % 20)}

which is the same as

    {"name" (fn [name] (includes? name "k")), "age" (fn [age] (< age 20))}

Then have another macro that converts that into the pattern matching code, or maybe there's already something in the standard library.

You could serialize the patterns using EDN as a substitute for JSON.

Fun stuff.

I wrote something [similar][1] in javascript. With that it would be:

    const is_k_kid = tisch.compileFunction((etc) => ({
      'name': name => name.includes('k'),
      'age': age => age < 20,
       ...etc
    }));
    const result = input.filter(is_k_kid);

Yes, "...etc" is part of the DSL.

[1]: https://github.com/dgoffredo/tisch