fnil

function

since v0.0-927

clojure.core/fnil

Edit

(fnil f x)

(fnil f x y)

(fnil f x y z)

Details:

Takes a function f, and returns a function that calls f, replacing a nil first argument to f with the supplied value x. Higher arity versions can replace arguments in the second and third positions (y, z).

Note that the function f can take any number of arguments, not just the one(s) being nil-patched.

Source docstring:

Takes a function f, and returns a function that calls f, replacing
a nil first argument to f with the supplied value x. Higher arity
versions can replace arguments in the second and third
positions (y, z). Note that the function f can take any number of
arguments, not just the one(s) being nil-patched.

Source code @ clojurescript:src/main/cljs/cljs/core.cljs

(defn fnil
  ([f x]
   (fn
     ([a] (f (if (nil? a) x a)))
     ([a b] (f (if (nil? a) x a) b))
     ([a b c] (f (if (nil? a) x a) b c))
     ([a b c & ds] (apply f (if (nil? a) x a) b c ds))))
  ([f x y]
   (fn
     ([a b] (f (if (nil? a) x a) (if (nil? b) y b)))
     ([a b c] (f (if (nil? a) x a) (if (nil? b) y b) c))
     ([a b c & ds] (apply f (if (nil? a) x a) (if (nil? b) y b) c ds))))
  ([f x y z]
   (fn
     ([a b] (f (if (nil? a) x a) (if (nil? b) y b)))
     ([a b c] (f (if (nil? a) x a) (if (nil? b) y b) (if (nil? c) z c)))
     ([a b c & ds] (apply f (if (nil? a) x a) (if (nil? b) y b) (if (nil? c) z c) ds)))))