World: r3wp

- Create references to parts of datatypes. Eg. Make a variable which 
aliases the y component of a pair!

Hum, we can with tiny functions accessors, the drawback is that it's 
more slow than a real reference

A pair! is a datatype which looks like a series, but is unfortunately 
(for this case) a scalar. That means any modification causes the 
whole pair to be copied.

I think I've found a good exercice...if only the following is true 
: Rebol seems to handle prefix notation

Operators can be prefix or infix

>> 2 + 3
== 5
>> + 2 3
== 5

Steeve, yes, you can do that, but then if other people want to use 
your code, they must use the accessors you have written, which effectively 
expands the language.

really strange : "+ 2 3" returns 5, but "- 2 3" returns 3

The - there is actually unary.

Yes, strange!

A negate.

ah yes. :-D

lol

It's the same as typing only  "2 3"

The 2 is evaluated (to 2), then the 3 is evaluated and returned, 
because it's last.

-2 3
 instead

Anton: that's it. So then  "+ 2 -3"

(Steeve, yes, more similar.)

- is the (only?) operator which cannot be used infix.

Sorry, that's an incorrect statement.

To get list of operators:

>> ? op!

Kib but for our sake, there is an infix version of - operator: subtract

You mean prefix.

- cannot be used as binary prefix operator, unlike the others + * 
/

Yes.

Steeve : thanks, i was just lookin for something like that

i don't like this name by the way, Carl should have renamed it: sub, 
since long time ago

I never use SUBTRACT because it's too long ! :-)  I always just use 
parens to allow me to use -, even if evaluation is slower.

Steeve : +1

Using parens, it's more clear this way.

sub suuuuuuuuuuuuuuuub ;-)

like in rebcode

Most operators have prefix only twins (that are called actions). 
Like: equals? is the twin of =

equal?

(without s)

multiply, add, subtract, divide, remainder, lesser?, lesser-or-equal?, 
not-equal?, equal?, strict-equal?, same?, greater?, greater-or-equal?

Geomol: power

beware with same? it's not really a math operator

If you prefer SUB instead of SUBTRACT, just do this in the beginning:

sub: :subtract

ah yes, POWER aslo.

*also*

I think, SAME? is like =?

yes but it's used for serie manipu

or objects, not for maths

>> [a b c] = [a b c]
== true
>> [a b c] == [a b c]
== true
>> [a b c] =? [a b c]
== false

oh my.... you should not bother Kib with same? too early ;-)

lol, he's bright, so he get it.

>> 1 = 1.0  
== true
>> 1 == 1.0
== false

Remember, if you wanna know more about operators like =, == and =?, 
just use ? to ask about them:

>> ? =?

It's fun doing these REBOL School sessions. It helps refresh the 
memories of us more experienced coders. It's hard (impossible) to 
remember all the corners of REBOL.

Geomol: in the last case 1 and 1.0 are different beasts because the 
first is integer and not the other, that's it ?