将哈希映射应用于Clojure中的匿名函数的快速方法

Question

My question is whether given a hashmap

(def my-map {'x 1 'y 2 'z})

I can apply it to an anonymous function,

(fn [xyz] (+ x (* yz))

so that the arguments match the keys in the map, somthing like

(apply-ish my-map (fn [xyz] (+ x (* yz)))

Is there an easy fix to this problem? I feel like there is but I cant figure it out.

Answer 1

You can use map destructuring:

user> (def my-map {'x 1 'y 2 'z 3})
#'user/my-map

user> ((fn [{x 'x y 'y z 'z}] (+ x (* y z))) my-map)
7

You can simplify a bit with this form of desctructuring:

user> ((fn [{:syms [x y z]}] (+ x (* y z))) my-map)
7

or if you use keywords for your map keys:

user> (def my-map2 {:x 1 :y 2 :z 3})
#'user/my-map2

user> ((fn [{:keys [x y z]}] (+ x (* y z))) my-map2)
7

Answer 2

personally, i would not modify the function to accept the map as the arg, since it makes the function itself way less generic. The alternative (and idiomatic i guess, for any language) solution is to select needed keys from the map before passing them to function. That is quite easy, since both map and symbol (and keyword too) have function semantics in clojure:

user> (apply f (map my-map ['x 'y 'z]))
;;=> 7

user> (apply f ((juxt 'x 'y 'z) my-map))
;;=> 7