No abstract

No abstract

No abstract

An implementation of APL is necessarily a rigid encoding of the rules of the language, including a de facto order in which expressions are evaluated. The order of execution is perceived in an APL program by the way in which side effects such as nested specification, specification of global variables within defined functions, and shared variable values affect the outcome of expressions.Concern about variation among implementations and distasteful results (see for example, "APL Problems with Order of Execution", Clark Wiedmann, in the March 1978 issue of Quote Quad) led to a proposed definition for the order of evaluation of APL expressions which received general acceptance at an APL implementors' workshop at Minnowbrook in September 1977.The refined "right to left" evaluation rule is examined and compared with other possible choices, through the use of simple APL syntax analysis models, to determine its implications on storage requirements, computation requirements, and mathematical identities. APL Order of Execution"In a compound expression such as (XxY+Z) -Q~'.R the order of execution of the elementary operations is determined by parentheses in the usual way and any remaining ambiguity is resolved from right to left, no priorities being accorded to multiplication or any other operator." [1] APL is a language with a relatively large number of primitive functions, and the preceding definition which prescribes that the order of execution be determined from context, was adopted as a simplification of conventional algebraic precedence rules because their extension to many functions would have been extremely complicated and impossible to remember. Although this definition precisely defines the order in which functions within a statement are to be evaluated, it leaves the order of evaluation of variables ambiguous.

An implementation of APL is necessarily a rigid encoding of the rules of the language, including a de facto order in which expressions are evaluated. The order of execution is perceived in an APL program by the way in which side effects such as nested specification, specification of global variables within defined functions, and shared variable values affect the outcome of expressions.Concern about variation among implementations and distasteful results (see for example, "APL Problems with Order of Execution", Clark Wiedmann, in the March 1978 issue of Quote Quad) led to a proposed definition for the order of evaluation of APL expressions which received general acceptance at an APL implementors' workshop at Minnowbrook in September 1977.The refined "right to left" evaluation rule is examined and compared with other possible choices, through the use of simple APL syntax analysis models, to determine its implications on storage requirements, computation requirements, and mathematical identities. APL Order of Execution"In a compound expression such as (XxY+Z) -Q~'.R the order of execution of the elementary operations is determined by parentheses in the usual way and any remaining ambiguity is resolved from right to left, no priorities being accorded to multiplication or any other operator." [1] APL is a language with a relatively large number of primitive functions, and the preceding definition which prescribes that the order of execution be determined from context, was adopted as a simplification of conventional algebraic precedence rules because their extension to many functions would have been extremely complicated and impossible to remember. Although this definition precisely defines the order in which functions within a statement are to be evaluated, it leaves the order of evaluation of variables ambiguous.