Retro-spec-ing a dataframe

retrospec.clj

=> (ns user (:require [powderkeg.sql :as sql] [clojure.spec :as s]))
=> (s/def ::age int?)(s/def ::name string?) (s/def ::friends (s/* ::name))
:user/age
:user/name
:user/friends

=> (sql/df [{:name "Gaël" :age 6 :friends ["Alix"]}
            {:name "Estelle" :age 4 :friends ["Léana"]}
            {:name "Lilly" :age 1 :friends ["Tigger" "Cuddly"]}]
     (s/keys :req-un [::name ::age ::friends]))
#object[org.apache.spark.sql.DataFrame 0x2f74149 "[name: string, age: bigint, friends: array<string>]"]

;; specs are preserved
=> (sql/spec-of *1)
(clojure.spec/keys
 :req-un
 [:user/name :user/age :user/friends])

=> (.registerTempTable *2 "kids")
nil

;; even through manipulations
=> (sql/exec "select name as `first-name`, age, size(friends) as `friends-count` from kids")
#object[org.apache.spark.sql.DataFrame 0x2d2d9b26 "[first-name: string, age: bigint, friends-count: int]"]
=> (sql/spec-of *1)
(clojure.spec/merge
 (clojure.spec/keys
  :req-un
  [:user/age])
 (powderkeg.sql/adhoc-map
  :first-name
  :user/name
  :friends-count
  clojure.core/int?))