maya.clj

## maya.clj
(ns maya)

(defmacro math->
  " (math-> 1 + 5 * 2 / 3) ;=> (-> 1 (+ 5) (* 2) (/ 3)) ;=> 4 "
  [exp & f-x-pairs]
  (if (even? (count f-x-pairs))
    `(-> ~exp
       ~@(for [[f x] (partition 2 f-x-pairs)]
           (list f x)))
    (throw (Exception. "f-x-pairs should be even."))))

(defmacro maya
  " (maya 1 + 5 :as six, six * 2 :as twelve, twelve / 3 * 2) ;=> 8 "
  [& exprs]
  (let [[exp [_ ?as & next-exprs :as E]] (split-with #(not= :as %) exprs)]
    (if (empty? E)
      (cons `math-> exp)
      `(let [~?as (math-> ~@exp)]
         (maya ~@next-exprs)))))

(comment
;-----
;Usage
;-----
(defn df [f]
  (fn [x]
    (maya 0.0001 :as dx, x + dx :as x+, (f x+) - (f x) / dx)))

(defn quadratic [a b c]
  (maya 4 * a * c :as d,
        b * b - d Math/pow 0.5 :as D,
        2 * a :as t, (- b) :as -b,
        -b + D / t :as x1,
        -b - D / t :as x2,
    [x1 x2]))

;------------------
;Python equivalents
;------------------
def df(f):
  def g(x):
    dx = 0.0001
    return (f(x+dx) - f(x)) / dx
  return g

def quadratic(a, b, c):
  d = 4 * a * c
  D = (b**2 - d) ** 0.5
  t = 2 * a
  return [(-b + D) / t, (-b - D) / t]
)