reduce

Takes a collection and a function, reduces the collection to a single result thanks to the function.

reduce [ '0', 1, 'b', 3 ]
  def result element
    result + element
# --> "01b3"

An initial value is accepted (generally after the collection)

reduce [ 0, 1, 2, 3, 4 ] 10
  def result i \ result + i
# --> 20

Passing a proc is OK too, but, in the case of a mathematical expression prefixing it with v. prevents premature rewriting...

reduce [ 0, 1, 2, 3, 4 ] 10 v.+
# --> 20

iterating and functions

Iterating functions accept 0 to 3 arguments when iterating over an array and 0 to 4 arguments when iterating over an object.

Those arguments are [ result, value, index, length ] for arrays. They are [ result, key, value, index, length ] for objects.

The corresponding res, key, val, idx and len variables are also set in the closure for the function call.