S3 (programming language)

S3

Paradigm	Structured, imperative
Developer	International Computers Limited
Influenced by
ALGOL 68

S3 is a structured, imperative high-level computer programming language. It was developed by the UK company International Computers Limited (ICL) for its 2900 Series mainframes. It is a system programming language with syntax influenced by ALGOL 68 but with data types and operators aligned to those offered by the 2900 Series. It was the implementation language of the operating system VME.

A rare example of an S3 program available in the public domain is the implementation of developed at the South-West Universities Regional Computer Centre, and archived in the Columbia University archive of Kermit implementations. The examples below are selected highlights of the main module (kmt_main_module).

The program starts with a module identification, and comments which we quote by way of acknowledgment to the authors:

Next follow a number of "mode declarations". Mode is the Algol 68 term for a type.

The first type is an array of 96 bytes; the next two are references (pointers) to arrays of bytes. KMT_MTM_VALUES is a union type allowing a variety of different types to appear. Note that WORD is a 32-bit unsigned integer, INT is a 32-bit signed integer; LONG makes it 64 bits. The last option in the union is marked REF()REF()BYTE, which means it is a pointer to an array whose members are pointers to arrays of bytes.

The final type declared here is a STRUCT, specifically a tuple containing two integers.

The program continues by declaring external procedures on which the module depends. RESPONSE indicates a return value containing error information:

and also some external variables:

The rest of the program consists of a number of procedure definitions. One of these, which actually defines the entry point to the program, is reproduced here:

Features to note here include:

...
Wikipedia