Seed7

Features

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

Major features include:

User defined statements and operators

Abstract data types

Templates without special syntax

OO with interfaces and multiple dispatch

Statically typed

May be interpreted or compiled

Source code portability

Runs under BSD, Linux, Mac OS X, Unix, Windows

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 times: 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 is based on UTF-32; this avoids the problems of a variable-length encoding like UTF-16.

The Seed7 project includes both an interpreter and a compiler. The interpreter starts programs very quickly. This supports fast program development. The 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.

Libraries

Seed7 has many libraries, which cover areas like containers, numeric functions, lexical analysis, file manipulation, networking (sockets, Transport Layer Security (TLS/SSL), Hypertext Transfer Protocol (HTTP), HTTP Secure (HTTPS), File Transfer Protocol (FTP), Simple Mail Transfer Protocol (SMTP), etc.), graphics, pixmap and vector fonts, database access (MySQL-MariaDB, SQLite, PostgreSQL, Oracle, Open Database Connectivity (ODBC)), Common Gateway Interface (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 needed to move Seed7 programs between different processors or operating systems.

History

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 precompiler, to translate MASTER to Pascal, was proposed, but unimplemented, 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 300,000 source 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;