Rebol
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Rebol
Just a quick look
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Philosophy
Rebol tries to be very simple to use, especially at first
Syntax is very simple, largely intuitive
Vocabulary can be quite large
Rebol depends on “dialects”: special-purpose vocabularies
for different kinds of tasks
Rebol is described as a “messaging language,” and has great
support for web and email
Data, including sounds and images, is represented as
characters
Elements
A Rebol program consists of three kinds of things:
Values, such as numbers, booleans, etc.
Blocks
Words represent things (such as variables) and actions (such as
functions)
Also comments--they begin with a semicolon ( ; )
There is no distinction between “code” and “data,” other than
what the program does with it
Rebol is interpreted, not compiled
A block is a list of things enclosed in square brackets, [ ], and
separated by white space
Blocks are evaluated only when the program says to evaluate them
Words
(but there’s a lot of “etc.”)
Values
Numbers: 5, 3.14, 1.2E7
Booleans: true, false
Hex: #{FF00FF}
Strings: "Hello world"
Characters: #"a"
Money: $4.99, EUR$4.99
URLs: http://google.com
Email: steve@apple.com
Files: %letter.txt
Dates: 8-Dec-2010
Times: 10:30AM
tags: <head>, </head>
tags: <head>, </head>
Tuples: 127.0.0.1
Pairs: 1024x768
Issues: 1-800-555-1212
Blocks: [red green blue]
There are about 45 types
Conversion functions are
to-type, e.g. to-char, to-hex,
to-image, etc.
Blocks
Blocks are things (values, words, other blocks)
enclosed in square brackets
There is no real distinction between code and data
[red green blue]
[if 2 < 4 [print 4]]
Thus, you can easily manipulate code
Implication: Functions--or any chunks of code--are first class
objects
Blocks are evaluated if the program evaluates them,
but not automatically
Words
There are five ways to use words:
As function names or variables: fun, value
Setting a word to a value: value: 5, foo: func [i] [i < 10]
Retrieving a value: :word
Useful for getting the value of a function
Using a word as a symbol, standing for itself: 'Bob-Smith
Using the word as a refinement: dump/hex, now/date
There are no reserved words
For example, you can redefine if
...but it’s probably not a good idea!
When executed: Call the function or return the value
Evaluating a block
do will evaluate a block and return the last value
reduce will evaluate a block and return a block of results
>> do [now/date colors [colors $12] 4]
== 4
>> data: reduce [now/date colors [colors $12] 4]
== [12-Dec-2002 [red green blue] [colors $12.00] 4]
Notice that only top-level elements are evaluated
If a block contains both code and data, compose will evaluate
only things within parentheses
>> compose [ now/date (now/date) ]
== [now/date 12-Dec-2002]
Control structures
do [...]
if expr [...]
either expr [...][...]
while [expr] [...]
for i min max step [...]
until [... expr]
loop count [...]
repeat var max [...]
forever [...]
switch/default var [ 1 [...] 2 [...] ] [...]
Logic
false or none
true or anything that isn’t false or none
and x y
or x y
not x
xor x y
all [...]
any [...]
< <= = == != <> >= >
Numbers
+, -, *, /, **, // (remainder)
exp value, log-10 value, log-2 value, log-e value, square-root
value
absolute value, negate value
min x y, max x y,
sine, cosine, tangent, arcsine, arccosine, arctangent
No precedence; evaluation is done left to right
Hence:
>> 2 + 3 * 10
== 50
Useful Functions
read source returns the string read from source (file, url, )
write dest data writes data to destination (file, url, )
ask question prompts the user the question, returns entered string
input read a line from the console
to-integer value converts value to an integer
to-date value converts value to a date
to-file value converts value to a filename
prin data prints data without line break
print data prints data, appends line break
foreach act list [...] executes the block for every element act in
list.
now returns current date/time
Defining functions
dump-i: [ print ["i =" i] ]
Not a function, just a block of code
>> i: 7
== 7
>> dump-i: [ print ["i =" i] ]
== [print ["i =" i]]
>> do dump-i
i=7
dump-i: func [][ print ["i =" i] ]
This is a “real” function
>> dump-i: func [][ print ["i =" i] ]
>> dump-i
i=7
Quick example: Text editor
view layout [
h1 "Text Editor:"
f: field 600 "filename.txt"
a: area 600x350
across
btn "Load" [
f/text: request-file
show f
a/text: read to-file f/text
show a
]
btn "Save" [
write to-file request-file/save/file f/text a/text
alert "Saved"
]
]
Quick example: Email client
view layout[
h1 "Send:"
btn "Server settings" [
system/schemes/default/host: request-text/title "SMTP Server:"
system/schemes/pop/host:
request-text/title "POP Server:"
system/schemes/default/user: request-text/title "SMTP User Name:"
system/schemes/default/pass: request-text/title "SMTP Password:"
system/user/email: to-email request-text/title "Your Email Addr:"
]
a: field "user@website.com"
s: field "Subject"
b: area
btn "Send"[
send/subject to-email a/text b/text s/text
alert "Sent"
]
h1 "Read:"
f: field "pop://user:pass@site.com"
btn "Read" [editor read to-url f/text]
]
99 Bottles of Beer on the Wall
sing: func [count rest] [
prin pick ["99 bottles " "no bottles " "1 bottle " [count "bottles "]]
min 4 count + 2
print rest
]
for bottles 99 0 -1 [
sing bottles "of beer on the wall,"
sing bottles "of beer."
print pick [
"Take one down, pass it around,"
"Go to the store, buy some more,"
] bottles > 0
sing bottles - 1 "of beer on the wall."
print ""
]
References
Rebol Quick Start, http://www.rebol.com/docs/quick-start.html,
by Carl Sassenrath, is a great introduction
Learn REBOL, http://www.re-bol.com/rebol.html, by Nick
Antonaccio, is a very good, and very thorough, tutorial
A Programming Tutorial for REBOL (PDF),
http://www.rebol.com/article/0201.html, by Victor Pavlu, is
thorough, but possibly a bit out of date
I got many examples from this tutorial
The recommended book is REBOL—A Programmer’s Guide, by
Olivier Auverlot and Peter William Alfred Wood
The End
