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Seed7 jeff hardy
Paradigm multi-paradigm, extensible, object-oriented, imperative, structured, generic, reflective
Designed by Thomas Mertes
First appeared 2005; 10 years ago (2005)
2015-01-18 / January 18, 2015; 4 months ago (2015-01-18)
static, strong, safe, nominative, manifest
OS Cross-platform (multi-platform) (Linux, Windows, Mac OS, BSD, Unix)
License GPL, LGPL (for the runtime library)
.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.[1] Seed7 supports the introduction of new syntax elements and their semantics into the language and it allows new language constructs to be defined using the Seed7 language itself.[2] E.g.: Programmers can introduce syntax and semantics of new statements as well as user defined operator symbols. The implementation of Seed7 differs significantly from the implementation of languages with hard-coded syntax and semantics.


Seed7 supports the imperative, object-oriented and generic programming paradigms. It also supports features such as call by name, multiple dispatch, function overloading, operator overloading, exception handling and arbitrary-precision arithmetic.

Major features include:

Several programming language concepts are generalized:

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 many libraries, which cover areas like containers, numeric functions, lexical analysis, file manipulation, networking (sockets, TLS/SSL, HTTP, HTTPS, FTP, SMTP, etc.), graphics, pixmap and vector fonts, database access (MySQL/MariaDB, SQLite, PostgreSQL, Oracle, ODBC), CGI support, data compression, character encoding, time and date handling, XML processing, message digests and more. This lowers the need to use operating system features and third party libraries directly. Seed7 libraries contain abstraction layers for hardware, operating system and third party libraries (e.g. graphic and database libraries). 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.[3][4] Most of the original ideas of MASTER, such as user defined statements and operators, can be found in Seed7. A precompiler, to translate MASTER to Pascal, was proposed. But this precompiler 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 2013-09-08 the Seed7 project contains more than 300000 lines of code and several hundred pages of documentation.

Extension mechanism[edit]

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.[1]

Syntax definition[edit]

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[edit]

The definition of the + operator for complex numbers is just a function definition:

const func complex: (in complex: summand1) + (in complex: summand2) is func
    var complex: sum is complex.value;
  begin := +; := +;
  end func;

Further reading[edit]

  • 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."


  1. ^ a b Zingaro, Daniel, "Modern Extensible Languages", SQRL Report 47 McMaster University (October 2007), page 16.
  2. ^ Abrial, Jean-Raymond and Glässer, Uwe, "Rigorous Methods for Software Construction and Analysis", ISBN 978-3-642-11446-5, Springer, 2010, page 166.
  3. ^ Mertes, Thomas, "Entwurf einer erweiterbaren höheren Programmiersprache", Diploma thesis Vienna University of Technology (1984).
  4. ^ Mertes, Thomas, "Definition einer erweiterbaren höheren Programmiersprache", Doctoral thesis Vienna University of Technology (1986).

External links[edit]