|Paradigm(s)||multi-paradigm, extensible, object-oriented, imperative, structured, generic, reflective|
|Designed by||Thomas Mertes|
|Stable release||2013-04-01 (April 1, 2013)|
|Typing discipline||static, strong, safe, nominative, manifest|
|Major implementations||open source reference implementation.|
|Influenced by||Pascal, Modula-2, Ada, ALGOL 68, C, C++, Java|
|OS||Cross-platform (multi-platform) (Linux, Windows, Mac OS, BSD, Unix)|
|License||GPL, LGPL (for the runtime library)|
|Usual filename extensions||.sd7, .s7i|
Seed7 is an extensible general-purpose programming language designed by Thomas Mertes. It is syntactically similar to Pascal and Ada. In addition to many other features it provides an extension mechanism. Seed7 supports the introduction of new syntax and their semantics into the language and it allows new language constructs to be defined using the Seed7 language itself. E.g.: Programmers can introduce syntax and semantic of new statements as well as user defined operator symbols. The implementation of Seed7 differs very much from the implementation of languages with hard-coded syntax and semantic.
Seed7 supports, besides the imperative, object-oriented and generic paradigm, also technologies like call by name, multiple dispatch, function overloading, operator overloading, exception handling and arbitrary-precision arithmetic. Several programming language concepts are generalized:
- Type declarations (which assign a name to a type) and function definitions take the form of constant definitions.
- Compile time expressions can execute user defined functions.
- Overloading and object-orientation (with multiple dispatch) are seen as common concepts. They just happen at different points of time (compile time and run time, respectively).
- Type names and type descriptions can be used as parameter and function result.
- Functions, which are executed at compile time, can be used to define objects.
- Templates are written as compile time functions with type parameters.
- Arrays, hash maps and structs are not a hard-coded feature. Instead they are defined as abstract data type in libraries.
- Parser and interpreter are part of the runtime library.
- Unicode support based on UTF-32 (this avoids the problems of a variable-length encoding like UTF-16).
- Source code portability.
The Seed7 project includes both an interpreter and a compiler. The interpreter starts programs very quickly. This supports fast program development. The Seed7 compiler uses the parser and reflection interfaces from the run-time library to generate a C program, which is subsequently compiled to machine code. Compiled Seed7 programs can have similar performance as C programs.
Seed7 has over 70 libraries, which cover areas like containers, numeric functions, lexical analysis, file manipulation, networking, graphics, pixmap and vector fonts, CGI support, character encoding, time and date handling and more. This lowers the need to use operating system features and third party libraries. Seed7 libraries contain abstraction layers for hardware and operating system. In other words: No changes are necessary, when Seed7 programs are moved between different processors or operating systems.
Seed7 is based on MASTER, an extensible programming language described in the diploma and doctoral theses of Thomas Mertes. Most of the original ideas of MASTER, such as user defined statements and operators, can be found in Seed7. A preprocessor for MASTER was proposed, but it was not implemented in the original project. In 1989, development began on an interpreter for MASTER, named HAL. In 2005, the MASTER and HAL projects were released as open source under the Seed7 project name. Since then new versions have been released every two or three weeks. As of version 2013-04-01 the Seed7 project contains more than 300000 lines of code and several hundred pages of documentation.
 Extension mechanism
An extension includes two parts: a syntax definition, giving a template for the new syntactic form, and a standard Seed7 function, used to define the semantics.
 Syntax definition
The syntax definition uses the Seed7 Structured Syntax Description (S7SSD). A S7SSD statement like
$ syntax expr: .(). + .() is -> 7;
specifies the syntax of the
+ operator. The right arrow
-> describes the associativity: Binding of operands from left to right. With
7 the priority of the
+ operator is defined. The syntax pattern
.(). + .() is introduced and delimited with dots (
.). Without dots the pattern is
() + () The symbol
() is a nonterminal symbol and
+ is a terminal symbol. The S7SSD does not distinguish between different nonterminal symbols. Instead it only knows one nonterminal symbol:
 Semantic extension
The definition of the
+ operator for complex numbers is just a function definition:
const func complex: (in complex: summand1) + (in complex: summand2) is func result var complex: sum is complex.value; begin sum.re := summand1.re + summand2.re; sum.im := summand1.im + summand2.im; end func;
 Further reading
- Abrial, Jean-Raymond; Glässer, Uwe (January 20, 2010). Rigorous Methods for Software Construction and Analysis (1 ed.). Springer Berlin Heidelberg. ISBN 978-3-642-11446-5.
- "To the best of our knowledge, among all these languages only the Seed7 programming
- language supports the introduction of new syntax and their semantics into the language."
- "In terms of language extensibility, Seed7 goes beyond CoreASM as it allows
- new language constructs to be defined using the Seed7 language itself."
- Zingaro, Daniel, "Modern Extensible Languages", SQRL Report 47 McMaster University (October 2007), page 16.
- Abrial, Jean-Raymond and Glässer, Uwe, "Rigorous Methods for Software Construction and Analysis", ISBN 978-3-642-11446-5, Springer, 2010, page 166.
- Mertes, Thomas, "Entwurf einer erweiterbaren höheren Programmiersprache", Diploma thesis Vienna University of Technology (1984).
- Mertes, Thomas, "Definition einer erweiterbaren höheren Programmiersprache", Doctoral thesis Vienna University of Technology (1986).
- Seed7 Homepage - Contains FAQ, manual, screenshots, examples, library descriptions and a collection of algorithms
- Seed7 at Rosetta Code - Contains many Seed7 examples
- Abstract of diploma thesis from Thomas Mertes in german
- Abstract of doctoral thesis from Thomas Mertes in german
- Doctorate thesis from Thomas Mertes in german
- Article from Daniel Zingaro, McMaster University, Hamilton, Ontario, Canada about "Modern Extensible Languages". (alternate link) (paragraph about Seed7 at page 16)
- Book from Abrial, Jean-Raymond and Glässer, Uwe: Rigorous Methods for Software Construction and Analysis (see Page 166)
- The Quest for the Ultimate Cycle explores the 3n+C extension of the Collatz Conjecture with Seed7 programs
- Blog by Remo Laubacher: Statically linked Linux executables with GCJ, Seed7 and haXe
- A FreeBSD port / see also here, maintained by Pietro Cerutti
- A Seed7 package for openSUSE/Fedora
- A discussion where Seed7 is described as language where new syntax can actually be defined by language users