Learning Ruby: methods vs procs (or Ruby vs Python?)

I have been meaning to learn ruby for a while and the place I am working now uses a lot so I had another look at it. I read Learn To Program, a simple but good book and found the bit on blocks and procs etc pretty good and wanted to see if I could do the stuff in Python as well. Python has anonymous “lambda” functions but they are limited to one line a subset of the syntax which is a bit annoying sometimes. My worry with methods in Ruby is that they are not first class, I think because you can omit parenthesis and so you have no way of referring to them without invoking them.

I remembered this while reading the SICP book, the question was about the difference between this program in applicative and normal order evaluation

(define (p) (p))

(define (test x y)
  (if (= x 0)

It rang a bell as (define (p) p) does not go into an infinite loop if you invoke p. In lisp (p) calls the procedure p with no arguments whereas p is just a reference to the function. In python someinstance.method refers to the method, someinstance.method() calls it, Ruby seems to need Proc objects to get around this (IMHO as a beginner)

I redid all the examples from the book in Python

Eg 1

Ruby “`ruby

def maybe_do some_proc if rand(2) == 0 some_proc.call end end

def twice_do some_proc some_proc.call some_proc.call end

wink = Proc.new do puts ’’ end

glance = Proc.new do puts ’’ end ”`

Python “`python import random

def maybe_do(some_proc): if random.choice(range(2)) == 0: some_proc()

def twice_do(some_proc): some_proc() some_proc()

def wink(): print ‘wink’

def glance(): print 'glance’

for i in range(5): print 'running for i=’,i maybe_do(wink) ”`


Ruby “`ruby

def do_until_false first_input, some_proc input = first_input output = first_input while output input = output output = some_proc.call input end input end

build_array_of_squares = Proc.new do |array| last_number = array.last if last_number <= 0 false else # Take off the last number… array.pop # …and replace it with its square… array.push last_number*last_number # …followed by the next smaller number. array.push last_number-1 end end

always_false = Proc.new do |just_ignore_me| false end

puts do_until_false([5], build_array_of_squares).inspect

yum = 'lemonade with a hint of orange blossom water’ puts do_until_false(yum, always_false) ”`

Python “`python def do_untill_false(first_input, some_proc): input = first_input output = first_input while output: input = output output = some_proc(input) return input

def build_array_of_squares(array): last_number = array.pop() if last_number <= 0: return False else: array.append(last_number * last_number) array.append(last_number - 1) return array

def always_false(just_ignore_me): return False

def just_ignore_me(): pass

print do_untill_false([5], build_array_of_squares) yum = 'lemonade with a hint of orange blossom water’ print do_untill_false(yum, always_false) ”`


Ruby “`ruby

def compose proc1, proc2 Proc.new do |x| proc2.call(proc1.call(x)) end end

square_it = Proc.new do |x| x*x end

double_it = Proc.new do |x| x+x end

double_then_square = compose double_it, square_it

square_then_double = compose square_it, double_it

puts double_then_square.call(5) puts square_then_double.call(5) ”`

Python “`python def compose(proc1,proc2): def composed(x): return proc2(proc1(x)) return composed

def square_it(x): return x**2

def double_it(x): return x*2

double_then_square = compose(double_it,square_it) square_then_double = compose(square_it,double_it)

print double_then_square(5) print square_then_double(5) ”`


class Array
  def each_even(&was_a_block__now_a_proc)
    # We start with "true" because
    # arrays start with 0, which is even.
    is_even = true
    self.each do |object|
      if is_even
        was_a_block__now_a_proc.call object
      # Toggle from even to odd, or odd to even.
      is_even = !is_even

fruits = ['apple', 'bad apple', 'cherry', 'durian']
fruits.each_even do |fruit|
  puts "Yum! I just love #{fruit} pies, don't you?"

[1, 2, 3, 4, 5].each_even do |odd_ball|
  puts "#{odd_ball} is NOT an even number!"

Python “`python class MyArray(list): def each_even(self): for i in range(len(self)): if i % 2 == 0: yield self[i]

fruits = MyArray(['apple’, 'bad apple’, 'cherry’, 'durian’])

for fruit in fruits.each_even(): print 'yum! I love %s pies, dont you?’ % fruit

for odd_ball in MyArray([1,2,3,4,5]).each_even(): print ’%s is NOT an even number’ % odd_ball ”`


Ruby “`ruby

def profile block_description, &block start_time = Time.new block.call duration = Time.new - start_time puts ”#{block_description}: #{duration} seconds" end

profile '25000 doublings’ do number = 1 25000.times do number = number + number end

puts “#{number.to_s.length} digits” # That’s the number of digits in this HUGE number. end

profile 'count to a million’ do number = 0 1000000.times do number = number + 1 end end Python python def profile(description, function): import time start_time = time.time() function() duration = time.time() - start_time print ’%s: %s seconds’ % (description, duration) print function.name print 'see, “function.name” can be used in place of description in python’

def count_to_a_million(): number = 0 for i in range(1000000): number = number+1

profile('count to a million’, count_to_a_million)

def profiled(function): def new_function(*args, **kwargs): import time start_time = time.time() result = function(*args, **kwargs) print function.name, 'took’, time.time() - start_time, 'secs’ return result return new_function

@profiled def count_to_a_million_again(): number = 0 for i in range(1000000): number = number + 1

count_to_a_million_again() “` This uses decorators, a nice Python feature that uses higher order functions (and the fact functions are first class in python).

In Conclusion

IMHO, at this point in my experience of Ruby, with all the disclaimers about my non expert status etc. Like:

  • No restriction on complexity of anonymous functions

Dont Like:

  • Methods being different from Procs/Blocs, non-uniform syntax
  • Leaving out parenthesis (though I await DSL goodness later!)
  • "end” everywhere (I know the indentation thing in python is contentious!)