From: Clemens Hintze <c.hintze@...>
Date: 2000-07-17T21:44:17+00:00
Subject: [ruby-talk:04096] Re: What are you using Ruby for?


> Aleksi Niemel writes:
> > Johann:

...

> This is one thing that I never quite understood about the "pure
> object-oriented languages"---they seem to dislike functions.
> Functions are very real things, quite useful in fact, but their a pain
> to manipulate, at least in Eiffel and Sather.

Hmmm ... I wouldn't say they dislike functions ... I think that
functions are not really necessary if I can have methods and closures!
They seem less powerful, IMHO, than the combination of these both ...

> As an example of what I do in python, I have a program which
> implements several functions over a dataset, then lets the user pick
> which functions to plot from the command line.  There are also
> multiple forms of each function, which are (in general) variable
> transformations.
> 
> The code looks like:
> 
> def make_g_from_f(f):
>   def temp(x, y, f=f):     # ugly python lack of closures
>     return f(x, y)*scale(x, y)
>   return temp
> 
> def f1(x, y):
>   return <something>
> register_function("f1", f1, "Compute something")
> 
> g1 = make_g_from_f(f1)     # useful python 1st-class functions
> register_function("g1", g1, "Compute something scaled by scale")

The closed (without thinking) I come at the first glance could be:

  def make_g_from_proc(f)
    return proc { |x, y| return f.call(x,y)*scale(x,y) }
  end
  
  def f1(x, y)
    return <something>
  end
  
  register_proc("f1", method(:f1), "compute something")
  
  g1 = make_g_from_proc(method(:f1))
  register_proc("g1", g1, "compute something scaled by scale")

This tries to resemble as much Python's solution as possible. The only 
big difference is that you have to pass a Proc instance to
make_g_from_proc ... So passing a method would need to get the method
first and convert it into a Proc instance! 

If I would use closures on all places where I would use a function in
Python, then I would even not have to convert a method to an Proc
instance ... something like:

  f1 = proc { |x, y| return <something> }
  register_proc("f1", f1, "compute someting")

  g1 = make_g_from_proc(f1)
  register_proc("g1", g1, "compute something scaled by scale")

...

> As I understand Ruby, I would have to make all of these functions into
> global Proc objects and use $-names to reference them, if I want f1
> and g1 to be callable using the same conventions.  That seems like it
> would get very ugly very fast.

If you insisting of same call convention and global accessible names,
perhaps! But no, wait a moment. There is a solution, not very elegant
but ...

  def f1
    return proc { |x, y| return <something> }
  end

  f1.call(1,2)
  register_proc "f1", f1, "compute something"

  g1 = make_g_from_proc f1
  register_proc "g1", g1, "compute something scaled by scale"

Now it looks equal and you have to use the same calling
convention. But I admit this is not too pretty ... Especially as
calling it via f1.call will do one indirection indeed! 

But I would try to solve this in a more OO way ... Using closures
resembling functions! Store them in a certain module/class that
indicates that these closures are thought to work on certain data for
computation ...

...

\cle