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