Macro Stuff

Generalized.clj

;;pass in a list of lists. Lists could contains N number of sub lists. Need an expression for each in each part of this function, 

(defn do-something [lol]
  (let [la (first lol)
        lb (second lol)]
     (map #(hash-map :a %1 :b %2)
       la, lb))
   

Something Like This.clj

  
(defprotocol FieldSpecifier
  (get-selector [_])
  (extract-field [_ node])
  (get-key [_]))


;; pass in a list of fields and be able to build selectors and extractors

(defrecord FieldSpec [key selector-key extractor-key]
  FieldSpecifier
  (get-selector [_] (selectors selector-key))
  (extract-field [_ node] ((extractors extractor-key) node))
  (get-key [_] key))

(defmacro select-fields [ns fields]
  (let [fcoll (var-get (resolve fields))
        build-syms (fn [prefix] (map #(-> % get-key gensym) fcoll))
        outer-syms (build-syms "outer")
        inner-syms (build-syms "inner")
        sym-to-sel (interleave outer-syms (map (fn [field] (get-selector field)) fcoll))
        hash-vals (interleave (map (fn [field] (get-key field)) fcoll) (map (fn [s] `(extract-field ~s)) inner-syms))]
    `(enlv/let-select
     ~ns [~@sym-to-sel]
     (map (fn [~@inner-syms] (hash-map ~@hash-vals))
          ~@outer-syms)))

Want This Form.clj

(defn select-subs [ns]
  (first
   (enlv/let-select
    ns [titles (selectors :sub-titles)
        times (selectors :sub-times)
        points (selectors :sub-points)
        users (selectors :sub-users)
        comments (selectors :sub-com-urls)]
    (map #(Submission.
           ((extractors :text) %1)
           ((extractors :url) %1)
           ((extractors :time) %2)
           ((extractors :num) %3)
           ((extractors :text) %4)
           ((extractors :url) %5)
           ((extractors :num) %5))
         titles times points users comments))))

Idea is that instead of selecting every field. The caller of select-fields can pass a collection of FieldSpecs and a form will be built containing only the desired fields.