[Rails] evaluating expressions left to right

[John Merlino]

class Proc
def apply(enum)
    enum.map &self
  end
  alias | apply

  def reduce(enum)
    enum.inject &self
  end
  alias <= reduce

def compose(f)
    if self.respond_to?(:arity) && self.arity == 1
      lambda {|*args| self[f[*args]] }
    else
      lambda {|*args| self[*f[*args]] }
    end
  end
  alias * compose

end

sum = lambda {|x,y| x+y }        # A function to add two numbers
mean = (sum<=a)/a.size           # Or sum.reduce(a) or a.inject(&sum)
deviation = lambda {|x| x-mean } # Function to compute difference from
mean
square = lambda {|x| x*x }       # Function to square a number
standardDeviation = Math.sqrt((sum<=square*deviation|a)/(a.size-1))

Ok so now I have another example from this book which does not contain
parentheses around deviation|a. So then why is this part:

(sum<=square*deviation|a)

not evaluated from left to right.

Apparently, it evaluates this part:

deviation|a

first

and this part second:

square*deviation|a

and then finally:

sum<=

So it looks like it is evaluating from right to left. Even though it
should be evaluating from left to right...



-- 
You received this message because you are subscribed to the Google Groups "Ruby 
on Rails: Talk" group.
To post to this group, send email to rubyonrails-talk@googlegroups.com.
To unsubscribe from this group, send email to 
rubyonrails-talk+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/groups/opt_out.