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List:       ruby-talk
Subject:    Re: Need examples comparing Ruby to Python
From:       "Jim Weirich" <jim () weirichhouse ! org>
Date:       2004-02-25 5:51:01
Message-ID: 34020.216.23.54.200.1077688256.squirrel () weirichhouse ! org
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Tobias Nurmiranta said:

> A difference between ruby and python is that functions can easily be
> passed as arguments in python. For example a function that returns the
> composition of two functions applied to a value. (An artificial example :)
>
> def compose(f, g, x):
>     return f(g(x))
>
> But then this is even more nicer i scheme.
>
> (defun (compose f g)
>   (lambda (x) (f (g x))) ;; returns a function, that can be applied later.
>
> ((compose 1+ 1+) 1) => 3

The Python and Scheme examples are a bit different.  The Scheme code
returns a newly created function that is the composition of two functions.
 The Python code merely returns the result of applying two functions to a
value.

The Scheme version in Ruby ...

  oneplus = lambda {|x| x+1 }
  def compose(f, g)
    lambda { |x| f[g[x]] }
  end
  compose(oneplus, oneplus) [1]   #=> 3

The Python version of compose is more like this ...

  def compose(f, g, x)
    f[g[x]]
  end

-- 
-- Jim Weirich     jim@weirichhouse.org    http://onestepback.org
-----------------------------------------------------------------
"Beware of bugs in the above code; I have only proved it correct,
not tried it." -- Donald Knuth (in a memo to Peter van Emde Boas)


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