Named argument example on 'function' documentation page about janet-lang.org HOT 2 CLOSED

# Any arguments following the function's required arguments are
# gathered into a struct and bound to the symbol following &keys.
((fn [&keys k] k)) # => {}
((fn [x y z &keys k] k) 1 2 3 :x 1 :y 2 :z 3) # => {:x 1 :y 2 :z 3}

# This combination of &keys and a symbol must be the last entry in the parameter tuple.
(fn [&keys k x]) # => compile error: &keys in unexpected location

# The compiler will not allow the simultaneous use of & and &keys.
(fn [& &keys k]) # => compile error: & in unexpected location

# The compiler will allow &opt to precede &keys, but in doing so all
# optional parameters become non-optional.
((fn [&opt o &keys k] [o k]) :x 1 :y 2) # => [:x {1 :y}]
((fn [&opt o &keys k] [o k]) 'shrug :x 1 :y 2) # => [shrug {:x 1 :y 2}]

# If any of the keyword arguments contain duplicate keys, the first
# occurrence of the key is used.
((fn [&keys k] k) :x 1 :x 2 :x 3) # => {:x 1}

# Example usage
(defn greet
  [name &keys {:greeting greeting}]
  (let [greeting (or greeting "Hello")]
    (print greeting ", " name "!")))

(greet "Janet") # => prints: Hello, Janet!
(greet "Janet" :greeting "Good morning") # => prints: Good morning, Janet!