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In article <1992Oct9.065708.25074@muddcs.claremont.edu> omitchel@jarthur.claremont.edu (Ocie *crow* Mitchell) writes:
>I was playing around with logo and I was wondering, how do you set the 
>value/type of a variable?
>
>[BASIC] x=10
>[C] int x=10
>[Logo] ?...
>

make "x 10

The answer
		make "x 12
is correct but really only answers part of the question.

In languages like BASIC and C, there is a heavy emphasis on the style of
programming in which instructions are executed in sequence, and most of
those instructions change the values of variables.  (In BASIC this is
because the language is not capable of any alternative; in C, it's because
the can't-teach-an-old-dog programmers aren't.)

In Logo it's not very common to use MAKE at all, or to change the value
of a variable in any other way.  Instead, Logo emphasizes functional
programming, in which the computation progresses when a function calls
another function.  (The function can call itself; that's recursion, which
Logo uses instead of conventional looping structures like WHILE.)

Example: Euclid's GCD algorithm, both ways:

------------------------------ C ------------------------------

int gcd(int a, int b)
{
    while (b != 0) {
	int temp = b;
	b = a % b;
	a = temp;
    }
    return a;
}

------------------------------ Logo ------------------------------

to gcd :a :b
if :b = 0 [output :a]
output gcd :b (remainder :a :b)
end

======================================================================

The point to notice is the complete absence of assignment instructions
in the Logo (recursive) version.  (Also, along with that, there's no
need for the extra variable temp.)  It would be possible to write it
the same way in C, but most C programmers wouldn't.

I hope I'm not insulting you by telling you things you knew already;
the original message didn't make that clear.

Hey Ocie, that wasn't such a silly question after all!

In <1b44g5INNqq1@agate.berkeley.edu> bh@anarres.CS.Berkeley.EDU (Brian Harvey) writes:

>The answer
>		make "x 12
>is correct but really only answers part of the question.

>In languages like BASIC and C, there is a heavy emphasis on the style of
>programming in which instructions are executed in sequence, and most of
>those instructions change the values of variables.  (In BASIC this is
>because the language is not capable of any alternative; in C, it's because
>the can't-teach-an-old-dog programmers aren't.)

>In Logo it's not very common to use MAKE at all, or to change the value
>of a variable in any other way.  Instead, Logo emphasizes functional
>programming, in which the computation progresses when a function calls
>another function.  (The function can call itself; that's recursion, which
>Logo uses instead of conventional looping structures like WHILE.)

>Example: Euclid's GCD algorithm, both ways:
>.....

This raises two questions:  First, Why does your book (*Computer Science 
Logo Style*) spend so much time on make and on "instruction sequence"
programs?  Second, how do you justify the abolition of assignment and
iteration to someone who is used to using them?  I don't mean the
fancy doctrines about denotational elegance and all that.  Few
programmers are interested in that stuff, assuming they can understand
it.  What are the *practical* advantages?

Incidentally, you probably should make it clear that you're talking
about a specific kind of recursion, namely tail recursion.  Most C
programmers will look at your Euclid's example, scratch their heads,
and say, "Gee, that's OK if you can set aside a meg for the stack.
These list guys sure don't know how to program in the real world...."
-- 

	ergo@netcom.com 			Isaac Rabinovitch
        {apple,amdahl,claris}!netcom!ergo	Santa Cruz, CA
	
	You will be assimilated.  Resistance is futile.
		

In article <1b44g5INNqq1@agate.berkeley.edu>, bh@anarres.CS.Berkeley.EDU (Brian Harvey) writes:
> The answer
> 		make "x 12
> is correct but really only answers part of the question.
> 

[ nice exposition on functional versus procedural programming deleted...]

BUT...

As one of those maligned C programmers (actually, I use C++ almost all the
time these days - hey, maybe he's not talking about me after all... :-),
I'm bothered by the casualness with which most FP people ignore the notion
of "state".

Oh well, never mind.  This discussion doesn't really belong here anyway.

Stan