Occam

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Occam
Paradigms : imperative , parallel
Publishing year: 1985
Designer: David May
Developer: Inmos Ltd.
Current  version : 2.1   ()
Dialects: occam-π
Influenced by: Communicating Sequential Processes

Occam is an imperative , parallel programming language based on Communicating Sequential Processes . It was developed around 1985 by David May among others at Inmos and is named after the philosopher and logician Wilhelm von Ockham (also Occam in English ). Their main focus is on the implementation of distributed systems , especially transputer systems. It was originally intended for INMOS microprocessors , but now also exists for other platforms.

Basic concept

Occam was named after Wilhelm von Ockham, as the approach of the language follows the principle of Occam 's razor . There are only five basic constructs in Occam: sequence, parallelism, alternative, condition and loop. Each of these constructs forms its own process, which consists of individual statements, which in turn represent processes themselves. The communication between the processes takes place via channels . A question mark ( ?) is used to read channels and an exclamation mark ( !) is used to output data on a channel. Comments are introduced with --and extend to the end of the line. Function blocks are combined by placing the same indent in front of each line . The two most important constructs sequence and parallelism should be briefly presented. The parallelism in particular distinguishes Occam from sequential programming languages ​​such as C , BASIC or Pascal .

sequence

A sequence is SEQinitiated with the keyword . Occam behaves like a conventional programming language within a sequence. 

SEQ
  EKanal ? a
  b := a * 5
  AKanal ! b

In the code fragment above, the value is first EKanalread from the channel and stored in the variable a . Then the variable is assigned bfive times the value of aand the variable is output bto the channel AKanal. The statements are processed one after the other (sequentially).

parallelism

Instructions to be processed in parallel are introduced with the keyword PAR. Every process it contains is started at the same time. 

PAR
  SEQ
    EKanal1 ? a
    EKanal2 ? b
    c := a * b
    AKanal1 ! c
  SEQ
    EKanal3 ? x
    EKanal4 ? y
    z := x + y
    AKanal2 ! z

The entire PARprocess consists of two SEQprocesses, which in turn consist of individual statements. The two SEQprocesses are PARstarted at the same time (because of their superordinate instructions) and processed in parallel.

Hello, World! in Occam 

PROC HelloWorld()
  []BYTE helloworldstring :
  SEQ
    helloworldstring := "Hello, World!"
    screen ! helloworldstring

literature

Web links