Rebol
Developer REBOL Technologies | | |
First appeared | 1997 | |
---|---|---|
Stable release | 2.7.8
/ January 2011 | |
Preview release | 2.101.0
/ December 2012 | |
cross-platform | ||
License | 2.7.8 is Freely redistributable software,[1] 2.101.0 has Apache 2.0 license[2] | |
Filename extensions | .r, .reb[3] | |
Website | www | |
Influenced by | ||
Self, Forth, Lisp, Logo[4] | ||
Influenced | ||
JSON,[5] Red | ||
|
Rebol (
Although it can be used for programming, writing functions, and performing processes, its greatest strength is the ability to easily create domain-specific languages or dialects
— Carl Sassenrath[8]
Douglas Crockford, known for his involvement in the development of JavaScript, has described Rebol as "a more modern language, but with some very similar ideas to Lisp, in that it's all built upon a representation of data which is then executable as programs" and as one of JSON's influences.[5]
Originally, the language and its official implementation were proprietary and closed source, developed by REBOL Technologies. Following discussion with Lawrence Rosen,[9] the Rebol version 3 interpreter was released under the Apache 2.0 license on December 12, 2012.[10] Older versions are only available in binary form, and no source release for them is planned.
Rebol has been used to program
Etymology
Rebol was initially an acronym for Relative Expression Based Object Language written in all caps.[6][8] To align with modern trends in language naming represented, e.g. by the change replacing historical name LISP by Lisp, programmers ceased the practice of writing REBOL in all caps. Sassenrath eventually put the naming question to the community debate on his blog.[11] In subsequent writing, Sassenrath adopted the convention of writing the language name as Rebol.[12]
History
First released in 1997, Rebol was designed over a 20-year period by Carl Sassenrath, the architect and primary developer of AmigaOS, based on his study of denotational semantics and using concepts from the programming languages Lisp, Forth, Logo, and Self.
- REBOL Technologies was founded in 1998.
- REBOL 2, the interpreter, which became the core of extended interpreter editions, was first released in 1999.
- REBOL/Command, which added strong encryption and ODBC access, was released in September 2000.
- REBOL/View was released in April 2001, adding graphical abilities on the core language.
- REBOL/IOS, an extensible collaboration environment built with REBOL was released in August 2001.
- REBOL/SDK, providing a choice of kernels to bind against, as well as a preprocessor, was released in December 2002.
- Rebol 3 [R3], the newest version of the interpreter, had alpha versions released by REBOL Technologies since January 2008. Since its release as an Apache 2 project in December 2012, it is being developed by the Rebol community.[13]
Design
Ease of use
One of the Rebol design principles is "to do simple things in simple ways".
view layout [text "Hello world!" button "Quit" [quit]]
This is how a similar example looks in R3-GUI:
view [text "Hello world!" button "Quit" on-action [quit]]
Dialects
Rebol
An example of Rebol's dialecting abilities can be seen with the word return
. In the data exchange dialect return
is just a word not having any specific meaning. In the do dialect, return
is a
A Rebol interpreter with graphical abilities must understand and interpret many dialects. The table below lists the most important ones in order of significance.
Dialect name | Interpreted by | Purpose |
---|---|---|
Data exchange dialect | load function
|
represents data and metadata; common platform for Rebol dialects |
Do dialect | do function
|
programming |
Parse dialect | parse function
|
pattern matching |
Function specification dialect | make function
|
function definition; functional programming
|
Object specification dialect | make function
|
object definition/inheritance; prototype-based programming |
Visual interface dialect (VID) or RebGUI |
layout functionor display function
|
specifies graphical user interface |
Draw dialect | view function
|
defines graphical elements (lines, polygons, etc.) |
Script specification dialect | do function
|
script definition |
Security policy dialect | secure function
|
specifies security policy |
Syntax
Rebol
Syntactic properties of different dialects may differ. The common platform for all Rebol dialects is the data exchange dialect; other dialects are usually derived from it. In addition to being the common platform for all dialects, the data exchange dialect is directly used to represent data and metadata, populate data structures, send data over Internet, and save them in data storage.
In contrast to programming languages like
Blocks as well as parens may contain other composite values (a block may contain subblocks, parens, strings, ...) or
a+b
is a word unlike a + b
, which is a sequence of three words separated by spaces.
Comments may appear following the semicolon until the end of the line. Multi-line comments or comments not ignored by the lexical parser can be written using "ordinary" datatypes like multi-line strings.[4]
Semantics
Blocks containing domain-specific language can be submitted as
do
The most frequently used evaluator is the do
function. It is used by default to interpret the text input to the interpreter
The do dialect interpreted by the do
function, is an
Words are used as
Subblocks of the root block evaluate to themselves. This property is used to handle data blocks, for structured programming by submitting blocks as arguments to control functions like if
, either
, loop
, etc., and for dialecting, when a block is passed to a specific interpreter function.[6]
A specific problem worth noting is that composite values, assigned to variables, are not copied. To make a copy, the value must be passed to the copy
function.[4]
The do
function normally follows a
abs -2 + 3
returns 1, since the infix addition takes precedence over the computation of the absolute value. When evaluating infix expressions, the order of evaluation is left to right, no operator takes precedence over another. For example,
2 + 3 * 4
returns 20, while an evaluation giving precedence to multiplication would yield 14. All operators have prefix versions. Do
usually evaluates arguments before passing them to a function. So, the below expression:
print read http://en.wikipedia.org/wiki/Rebol
first reads the Wikipedia Rebol page and then passes the result to the print
function. Parentheses can be used to change the order of evaluation. Using prefix notation, the usage of parentheses in expressions can be avoided.[4]
The simple precedence rules are both an advantage:
- No need to "consult" precedence tables when writing expressions
- No need to rewrite precedence tables when a new operator is defined
- Expressions can be easily transliterated from infix to prefix notation and vice versa
as well as a disadvantage:
- Users accustomed to more conventional precedence rules may easily make a mistake[6]
parse
The parse
function is preferably used to specify, validate, transform and interpret dialects. It does so by matching parse expressions at run time.[6]
Parse expressions are written in the parse dialect, which, like the do dialect, is an expression-oriented sublanguage of the data exchange dialect. Unlike the do dialect, the parse dialect uses keywords representing operators and the most important
Actions can be included to be taken during the parsing process as well and the parse
function can be used to process blocks or strings. At the string parsing level parse
must handle the "low level" parsing, taking into account characters and delimiters. Block parsing is higher level, handling the scanning at the level of Rebol values.[6]
The parse dialect belongs to the family of grammars represented by the top-down parsing language or the parsing expression grammar (PEG). The main similarity is the presence of the sequence and choice operators all the family members have. Parse dialect syntax and the similarities between the parse dialect and the PEG are illustrated by this transliteration of a PEG example that parses an arithmetic expression:
Digit: charset [#"0" - #"9"]
Value: [some Digit | "(" Expr ")"]
Product: [Value any [["*"| "/"] Value]]
Sum: [Product any [["+"| "-"] Product]]
Expr: Sum
parse/all "12+13" Expr
Implementations
The official Rebol 2.7.8 implementation is available in several editions (/Core, /View, /Command, /SDK and /IOS). Both /Core and /View editions are freely redistributable software.[1]
The runtime environment is stored in a single executable file. Rebol/Core 2.7.8, the console edition, is about 300 KB and Rebol/View 2.7.8, the graphical user interface edition, is about 650 KB in size.
Rebol/View provides
Legacy
- Rebol was named by JavaScript Object Notation.[5]
- Rebol inspired the open-source Orca project, which is an interpreted Rebol-like language.[14]
- Boron is an interpreted, homoiconic language inspired by and similar to Rebol, which is meant for embedding domain specific languages. It is implemented as a C library licensed under the terms of the LGPLv3.
- The Red programming language was directly inspired by Rebol, yet the implementation choices of Red were geared specifically to overcoming its perceived limitations.[15]
See also
References
- ^ a b REBOL Technologies. The REBOL/View and REBOL/Core 2.7.8 license
- ^ R3 source at GitHub
- ^ "Carl's REBOL Blog - Let's switch to .reb suffix". Rebol.com. August 18, 2013. Retrieved January 23, 2014.
- ^ ISBN 0-07-212279-X.
- ^ a b c Crockford, Douglas. The JSON Saga, jsonsaga.ppt Archived October 4, 2012, at the Wayback Machine
- ^ ISBN 0-7645-0745-1.
- ^ ISBN 2-212-11017-0.
- ^ a b Sassenrath, Carl (July 1, 2000). "Inside the REBOL scripting language". Dr. Dobb's Journal.
- ^ "REBOL to become open source". Rebol.com. September 25, 2012. Retrieved January 23, 2014.
- ^ Sassenrath, Carl (December 12, 2012). "Comments on: R3 Source Code Released!". Retrieved August 14, 2014.
You probably thought the source release would never happen? Am I right? Well, it's there now in github at github.com/rebol/rebol.
- ^ "Calling REBOL Rebol?". December 14, 2012. Archived from the original on December 3, 2013. Retrieved December 2, 2013.
- ^ Sassenrath, Carl. "Cross-compiling Rebol for your favorite embedded board". Retrieved September 16, 2016.
- ^ "Source code for the Rebol interpreter". rebol/rebol GitHub. Retrieved March 14, 2017.
- ^ The rebol-orca project at Freecode
- ^ The Red project at GitHub
Further reading
- Mikes, Nora (November 20, 1999). "A REBOL incursion: It's not a scripting language, not a programming language -- and not a new Amiga, either. Or is it?". LinuxWorld. Archived from the original on March 24, 2005.
- Story, Derrick (August 27, 1999). "Rebol Might Be the Language for the Rest of Us". Web Review. Archived from the original on October 12, 1999.