Execution model: Difference between revisions

Revision as of 00:11, 7 March 2019

Revision as of 08:21, 17 March 2019

Line 1:

{{Program execution}}

InA softwareprogramming programlanguage execution,consists of a grammar/syntax plus an '''execution model'''. specifies howThe execution model specifies the programbehavior [[executionof (computing)|execution]]elements takesof placethe language. EveryBy [[programmingapplying language]]it, hasone ancan executionderive model,the whichbehavior isof specifieda asprogram partthat was written in terms of thethat programming language. For specificationexample, and[[Operational_semantics| isOperational implementedSemantics]] asis partone method of thespecifying a language's implementationexecution model. The detailsobserved inbehavior of a running program must match the specificationbehavior ofderived anfrom the execution model. An execution model covercovers things such as what is an indivisible unit of work, and what are the constraints on the order in which those units of work take place. For example, the addition operation is an indivisible unit of work in many languages, and in sequential languages such units of work are constrained to take place one after the other.

In particular, the [[C (programming language)|C programming language]], has a concept called a statement. The spec says that a statement is a chunk of syntax that is terminated by a ";". The language spec then says that execution of the program proceeds statement by statement, which tells us something about the execution model of the language. It tells us that statements are indivisible units of work and that they proceed in the same order as their syntactic appearance in the code (except when a control statement such as IF or WHILE modifies the order). By stating the order in which statements are executed, the language spec has stated constraints on the order of performing units of work. The C language actually has an additional level to its execution model, which is the order of precedence. It states the rules for the order of operations within a single statement. The order of precedence can be viewed as stating the constraints on performing the units of work that are within a single statement. So, ";" and "IF" and "WHILE" cover constraints on the order of statements, while order of precedence covers constraints on work within a statement. Hence, these parts of the C language specification are stating the execution model of the C language.