在Ruby中获取Lisp样式加法（+ * args）的最简单方法是什么？

Question

So I really like this syntax in Lisp:

 (+ 1 1 2 3 5 8 13)
 => 33

I want to add a list of items in Ruby and would like to approximate this as best as possible. Right now, my best solution involves an array and the collect/map method.

So:

sum = 0; [1,1,2,3,5,8,13].collect { |n| sum += n }

BUT...

I would like to add methods to this which could return nil.

sum = 0; [1, booking_fee, 8,13].collect { |n| n = 0 if n.nil?; sum += n }

And it would be really nice to do this, where all of the lines in the middle refer to methods that may return nil, but I can't exactly build an array in this manner. This is just an idea of what I want my syntax to look like.

def total
  Array.new do
    booking_fee
    rental_charges
    internationalization_charges
    discounts
    wild_nights
  end.collect { |n| n = 0 if n.nil?; sum += n }
end

Any suggestions before I try to hack away and effectuate Greenspun's Rule? (Programming is indeed a compulsion.

Answer 1

I really don't understand your question. If you want a method that works like + does in Lisp, ie takes an arbitrary number of arguments and is in prefix position rather than infix, that's trivial:

def plus(*nums)
  nums.inject(:+)
end

plus 1, 1, 2, 3, 5, 8, 13 # => 33

If you want to get really fancy, you could override the unary prefix + operator for Array s:

class Array
  def +@
    inject(:+)
  end
end

+[1, 1, 2, 3, 5, 8, 13] # => 33

Please don't do that!

I don't see how the rest of your question is related in any way to a Lisp-style addition operation.

If you want to remove nil s from an Array , there's Array#compact for that.

Answer 2

• There is already a method inject for doing what you want.
• Changing nil to a number without affecting a number is easy: use to_i (or to_f if you are dealing with float).

.

[
  booking_fee,
  rental_charges,
  internationalization_charges,
  discounts,
  wild_nights,
].inject(0){|sum, item| sum + item.to_i}