World: r3wp

In the classes in astronomy, we're taught a language called IDL to 
reduce scientific data and make images and diagrams. I often just 
use REBOL directly to make the diagrams. I've wanted many times to 
make a library of routines or a plotting application in REBOL, but 
haven't had the time yet. Maybe some day.

When it comes across a lit-word!, however, it reduces it to the word! 
of the same spelling.

This is how I think of it:

	lit-word!  -->  word!  -->  value

Anton: ok, that's clearer now.

Geomol: is creating a plotting dialect that hard ?

try this Kib:
>> a: 2
>> reduce [a]
>> reduce ['a]

and
>> reduce reduce ['a]

I wouldn't mind being able to set 3-4 months aside to create a complete 
graphing dialect.

Steeve: ok i've tried. But why the reduce output is a block ?

(kib2: yes, creating a plotting dialect is hard. It must be - I tried 
creating a general plotting function. There are many types of chart/graph 
to support.)

kib, it's probably not hard, maybe take a bit of work to make it 
really slim and clever. I just have a ton of projects in the air 
all the time, so I didn't come to it yet.

Geomol: not as much as Carl !

Kib because the input of reduce is a block

Try this:
	reduce ['print join "bon" "jour"]

That is simply how reduce works. If you want a single value output, 
then use DO, which returns the last evalated value in the block.
	do ['a]

Anton: funny

in fact it's logical : everything is a block.

REDUCE is one of several block manipulation functions. It evaluates 
anything that can be evaluated inside a block.

even, you can do 
>> reduce 'a

ahahah

REDUCE is not restricted to blocks.

Yes, if you type something in the console, eg:

	print 1 + 2


you can imagine that it takes the string "print 1 + 2", LOADS it 
into a block, [print 1 + 2], then DOes it.

Steeve: yes, i've tried, but it's limited to the word behind reduce 
then ?

not now, but in the past, it was

DO is like REDUCE, in that it evaluates every item in the block, 
except DO does not create and store results in a new block - it just 
returns the last value.

yes Kib, blocks are mainly used to pass several value

understood, now the question is what we cannot do in Rebol ?!

You can't really say that in rebol everything is a block, but you 
can say everything is *in* a block. Most rebol code is found in blocks. 
Blocks rule as the container of choice in the rebol universe!

What we cannot do in rebol:

i will say, what we cannot do without pain. All is possible but some 
are painfull

- 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!