docprint.clj

(ns prndoc.core
  (require 
    [clojure.core.strint :refer [<<]]
    [clojure.core.match :refer [match]]))

(defn has-splat? [arglist]
  ((complement nil?) (first (last (split-with #(not= % '&) arglist)))))

(defn parse-arg-pattern
  "Argument pattern [num-args has-splat?]. Pattern of [func & body] is [1 true]."
  [arglist]
  (if
    (has-splat? arglist) [(- (count arglist) 2) true] [(count arglist) false]
    )
)

(defn match-arglist
  "Find the matching arglist."
  [arglists args]
  
    (first (filter #(or (= (parse-arg-pattern args) (parse-arg-pattern %))
                        (and (= (last (parse-arg-pattern %)) true) (> (first (parse-arg-pattern args)) (first (parse-arg-pattern %))))) arglists))))

(defn arg-bindings
  "Return bindings of form [n 4 members []]"
  [arglists args]
  (let [arglist (match-arglist arglists args)
        [num-args splat?] (parse-arg-pattern arglist)
        split-args (split-at num-args args)]
    (if splat? (vec (interleave (filter #(not= '& %) arglist) (conj (vec (first split-args)) (vec (last split-args))))) 
               (vec (interleave arglist args)))
    ))

(defn docprint-decorator
  "Print a function's docstring at runtime, with interpolated values of args."
  [m# f]
  (fn [& args]
    (do 
      (eval `(let ~(arg-bindings (:arglists m#) args) (prn (<< ~(:doc m#)))))
      (apply f args))))


(defmacro docprint!
  "Apply docprint decorator to function. Do not apply more than once."
  [sym]
  `(let [m# (meta (var ~sym))]
     (when (not= true (:docprint m#))
       (def ~sym ((partial docprint-decorator m#) ~sym))
       (reset-meta! (var ~sym) (assoc m# :docprint true))) 
     (var ~sym)))

; toy functions
(defn elect-n
  "Electing ~{n} members to a group"
  ([n] (elect-n n []))
  ([n members] members)
  ([n members & options] members)
)

(defn accept-many-args
  "This function was called with ~(count more) additional arguments, ~(+ 2 (count more)) in total."
  [n1 n2 & more])

(defn add-two
  "Adding ~{a} to ~{b}."
  [a b]
  (+ a b))

(docprint! accept-many-args)
(docprint! elect-n)
(docprint! add-two)

(do 
  (accept-many-args 1 2 3 4 5 6 7 8 9 10) 
  (elect-n 5 [])
  (add-two 1 2))

;has-splat?
  (= false (has-splat? '[n members]))
  (= true (has-splat? '[func & body]))

;match-arglist
  (= '[n]                   (match-arglist '([n] [n members] [n members & options]) '(4)))
  (= '[n members]           (match-arglist '([n] [n members] [n members & options]) '(4 [])))
  (= '[n members & options] (match-arglist '([n] [n members] [n members & options]) '(4 [] "fred")))   

;parse-arg-pattern
  (= [1 true] (parse-arg-pattern '[func & body]))
  (= [2 false] (parse-arg-pattern '[n members]))
  
;arg-bindings
  (= '[n 4] (arg-bindings '([n] [n members] [n members & options]) '(4)))
  (= '[n 4 members []] (arg-bindings '([n] [n members] [n members & options]) '(4 [])))
  (= '[n 4 members [] options (1 2)] (arg-bindings '([n] [n members] [n members & options]) '(4 [] 1 2)))