REBOL 3 Concepts: Expressions: Values

REBOL provides a built-in set of values that can be expressed and exchanged between all systems. Values are the primary elements for composing all REBOL expressions.

Contents

Direct and Indirect Values

Values can be directly or indirectly expressed.

A directly expressed value is known as it is lexically, or literally, written. For instance, the number 10 or the time 10:30 are directly expressed values.

An indirectly expressed value is unknown until it is evaluated. The values none!, true, and false all require words to represent them. These values are indirectly expressed because they must be evaluated for their values to be known. This is also true of other values, such as lists, hashes, functions, objects.

Datatypes of Values

Every REBOL value is of a particular datatype. The datatype of a value defines:

1. The range of possible values for the datatype. For example, the logic datatype can only be true or false.
2. The operations that can be performed. For example, you can add two integers, but you cannot add two logical values.
3. The way in which the values are stored in memory. Some datatypes can be stored directly (such as numbers), while others are stored indirectly (such as strings).

By convention, REBOL datatype words are followed by an exclamation point (!) to help make them stand out. For example:

integer!
char!
word!
string!

Table of common datatypes

1234 -432

3.1415 1.23E12 0,01 1,2E12

1% 100% 12.34% 1234%

$12.34 USD$12.34 CAD$123.45 DEM$1234,56

12:34 20:05:32 -0:25.34

20-Apr-1998
20-4-1998
20-Apr-1998/12:32        ; date and time
20-Apr-1998/12:32-8:00   ; with timezone

3.1.5           ; version numbers
255.255.0.100   ; RGBA colors
199.4.80.7      ; Internet addresses

5x10 100x100 -50x-25

"Here is a string"
{Here is another way to write
a string that spans many lines
and contains "quoted" strings.}

#{0A6B14728C4DBEF5}      ; hex encoded
64#{45kLKJOIU8439LKJklj} ; base-64 encoded

<title> </body>
<font size="2" color="blue">

info@rebol.com
bill-smity@example.com

%data.txt
%images/photo.jpg
%../scripts/*.r

http://www.rebol.com
ftp://ftp.rebol.com/sendmail.r
mailto:info@rebol.com

#707-467-8000        ; a phone number
#0000-1234-5678-9999 ; a credit card number
#MFG-932-741-A       ; a model number