clojure defn pattern matching

2018-06-29 14:01:12

I am really new to clojure, and I want to simulate + from clojure, I wrote something like this:

(defn sum
  ([] 0)
  ([x & xs] (+ x (sum xs))))
(sum 1 2 3 4) ; ERROR

which is not right, as in Haskell, I can write

sum' :: [Int] -> Int
sum' [] = 0
sum' (x:xs) = x + sum' xs

What is the problem with the clojure code ? Thanks!

Correct would be as follows:

(defn sum
    ([] 0)
    ([x & xs] (+ x (apply sum xs))))

You were calling the function with one argument, a list, thus hitting the second case over and over until recursion depth exceeded.

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