Applying sequence of functions to a sequence of values

Question

I want to pairwise apply a list of functions to a list of values.

Here's an example to illustrate.

user=> (defn a [f x] (f x))
#'user/a
user=> (map a [inc dec] '(98 8))
(99 7)

Notice I had to define a function a that takes a function and applies it to a value. Basically abstracting function application.

Is there a more natural way to do this? I would really just like to use map with defining a helper function.

Answer 1

You can always define functions anonymously, inline:

(map (fn [f x] (f x)) [inc dec] '(98 8))

or shorter, using the #() reader macro:

(map #(%1 %2) [inc dec] '(98 8))

It's a fairly awkward use case though, so I doubt you can reduce it to something shorter using just core clojure or clojure.contrib, but you can easily write your own abstraction:

(defn mapfs [fs coll] (map #(%1 %2) fs coll))
(mapfs [inc dec] [98 8])
> (99 7)

Answer 2

If you're willing to slightly modify the format of your values, things get a bit simpler:

user=> (map apply [inc dec] [[98] [8]])
(99 7)

It's necessary because apply must have a seq as its last argument. This transformation ([98 8] => [[98] [8]]) feels like a reasonable thing to do anyway, since otherwise you depend on the fact that the functions may only take one value apiece. It's of course trivial to do:

user=> (map list [98 8])
((98) (8))

Otherwise, Joost's mapping function #(%1 %2) is as concise as you're going to get.