class Proc
A block or a lambda as a value, of a type (A, B) -> R: called with
call, () or [].
<prelude>:5141
Methods
def arity -> Int
The number of parameters: -n - 1 when there are optional ones or a
rest parameter after n required ones, as in Ruby. A method reference
(obj.:name) gives -1.
->(a: Int, b: Int) { a + b }.arity # => 2
->(a: Int, b: Int = 2) { a + b }.arity # => -2
<prelude>:5151