From: Florian Gross <flgr@...>
Date: 2004-07-14T07:22:21+09:00
Subject: Re: Functional Ruby (Re: Why I don't use Ruby.)

Sean O'Dell wrote:

>>>>> You're not supposed to have operators in a functional
>>>>> language, like =, *, + and so on,
>>>> BTW, an operator is usually nothing more than syntactic sugar
>>>> for a function call.
>>> No, functional languages are not supposed to have operators.
>>> That's why they're called "functional languages"; they work like
>>> functions.
>> Most of those operators are exactly like functions. = isn't if its
>> an assignment operator, but if it is an comparison operator it
>> indeed is compatible to the definition of the function. (Just
>> because there's a different syntax for applying it doesn't mean 
>> that it's really different -- in fact in LISP + is just a function
>> with a special name without any additional syntactic sugar.)
> I know, but I was trying to illustrate how some people seem to get
> the rule against assignment operators confused with simple
> assignment.  You can assign values to variables in a functional
> language, you just have to do it through a function call; the
> assignment is permitted, however.  We're in agreement.

I'm not sure we're that rule is coming from -- do you remember any
sources for this or could you try to explain why it exists for yourself?

I've not seen it before -- I think the only restriction about all this
is that assignment is only a way of aliasing functions or results of
function calls, but nothing more than a notation. (Which means that it
doesn't really give any more power to you than you already had without it.)

>>>>> so you can't assign values "a=10" style, but you should be
>>>>> able to say set(a, 10).
>>>> Where is exactly the difference from a semantic POV ?
>>> Functional languages set the variable in a functional way.
>> Functional languages don't enforce a specific syntax like
>> function(arg1, arg2) etc., but they indeed specify that a function
>> should have no side effects which means that the only way it should
>> be able to interact with the outside world is by returning values.
>> (Lambda calculus is the origin of functional languages and compared
>> to computer languages its syntax is indeed very exotic.)
> Unless something has changed, functional languages DO have to enforce
> a specific syntax; it must be functional (call, parameter).  The
> precise syntax is up to each language; lisp does it something like
> (set a 10) I believe, but another language could do it set(a, 10).
> It really doesn't matter.

Well, all you need to do is providing a way to define and apply
functions and some basic built-in functions to make the language
turing-complete. (Unlambda states that only the K- and S-combinators are
needed for defining a turing-complete language, but I still don't
understand this completely.)

I'm not sure if we're saying the same or something different regarding
this point. :)

>> I hope I was able to add something valuable.
> The only real rule about assignment, I believe (been a long time), is
> that it must be in a functional form, and operators are not allowed
> (can't do a=10).

Why? Where's the difference? :)

Regards,
Florian Gross