Re: [stack] Point free (pointless) programming in ruby? (fwd)

On Jan 13, 2009, at 6:15 PM, John Carter wrote:

> 1) Is there a neater way of expressing a sequence of function
>    compositions in Ruby?

Evaluation of a concatenative language is just a fold of 'apply' over  
your list of functions with the empty list as the initial element. For  
example, in Scheme:

    (define (ceval fs) (fold apply '() fs))

Your Ruby version is essentially the same thing.

> 2) Which Ruby Pointfree sequences are actually useful?

All you can really do is implement a concatenative language inside  
Ruby complete with its own standard library. This is probably not so  
useful.

Languages like ML and Haskell work better because they have curried  
functions. There even exists a tool for automatically translating  
pointful Haskell functions to point-free Haskell functions, although  
the results are often less than clear:

    \x y z -> y * z - x  ==  flip (flip . ((-) .) . (*))

You may want to look at the following:
http://www.haskell.org/haskellwiki/Pointfree

Keep in mind that all existing concatenative languages make heavy use  
of stacks. Related languages like FP and FL make heavy use of lists.  
Trying to do pointfree programming in languages that don't do such  
things (Ruby, Python, Haskell, Scheme, etc) is going to be quite  
painful. For example, here's the Haskell example above in Joy:

    * swap -

And in a concatenative FP-style language:

    - [hd, * tl]

- John