Function-declarations

function-declaration = function-heading ';' directive

½ function-identification ';' function-block

½ function-heading ';' function-block .

function-heading = 'function' identifier [ formal-parameter-list ] ':' result-type .

function-identification = 'function' function-identifier .

function-identifier = identifier .

result-type = simple-type-identifier ½ pointer-type-identifier .

function-block = block .

The occurrence of a formal-parameter-list in a function-heading of a function-declaration shall define the formal-parameters of the function-block, if any, associated with the identifier of the function-heading to be those of the formal-parameter-list. The function-block shall contain at least one assignment-statement such that the function-identifier of the assignment-statement is associated with the block (see 6.8.2.2).

The occurrence of an identifier in the function-heading of a function-declaration shall constitute its defining-point as a function-identifier associated with the result type denoted by the result-type for the region that is the block closest-containing the function-declaration.

Each identifier having a defining-point as a function-identifier in the function-heading of a function-declaration in which the directive forward occurs shall have exactly one of its applied occurrences in a function-identification of a function-declaration, and this applied occurrence shall be closest-contained by the procedure-and-function-declaration-part closest-containing the function-heading.

The occurrence of a function-block in a function-declaration shall associate the function-block with the identifier in the function-heading, or with the function-identifier in the function-identification, of the function-declaration; the block of the function-block shall be associated with the result type that is associated with the identifier or function-identifier.

There shall be at most one function-block associated with a function-identifier.

Example of a procedure-and-function-declaration-part:

function Sqrt (x : real) : real;

{This function computes the square root of x (x > 0) using Newton's method.}

var

old, estimate : real;

begin

estimate := x;

repeat

old := estimate;

estimate := (old + x / old) * 0.5;

until abs(estimate - old) < eps * estimate;

{eps being a global constant}

Sqrt := estimate

end {of Sqrt};

function max (a : vector) : real;

{This function finds the largest component of the value of a.}

var

largestsofar : real;

fence : indextype;

begin

largestsofar := a[1];

{ Establishes largestsofar = max(a[1]) }

for fence := 2 to limit do begin

if largestsofar < a[fence] then largestsofar := a[fence]

{ Re-establishing largestsofar = max(a[1], ... ,a[fence]) }

end;

{ So now largestsofar = max(a[1], ... ,a[limit]) }

max := largestsofar

end {of max};

function GCD (m, n : natural) : natural;

begin

if n=0 then GCD := m else GCD := GCD(n, m mod n);

end;

{The following two functions analyze a parenthesized expression and convert it to an internal form.

They are declared forward since they are mutually recursive, i.e., they call each other.

These function-declarations use the following identifiers that are not defined in this International

Standard: formula, IsOpenParenthesis, IsOperator, MakeFormula, nextsym, operation, ReadElement,

ReadOperator, and SkipSymbol.}

function ReadExpression : formula; forward;

function ReadOperand : formula; forward;

function ReadExpression; {See forward declaration of heading.}

var

this : formula;

op : operation;

begin

this := ReadOperand;

while IsOperator(nextsym) do

begin

op := ReadOperator;

this := MakeFormula(this, op, ReadOperand);

end;

ReadExpression := this

end;

function ReadOperand; {See forward declaration of heading.}

begin

if IsOpenParenthesis(nextsym) then

begin

SkipSymbol;

ReadOperand := ReadExpression;

{nextsym should be a close-parenthesis}

SkipSymbol

end

else ReadOperand := ReadElement

end;

Parameters

General

The identifier-list in a value-parameter-specification shall be a list of value parameters. The identifier-list in a variable-parameter-specification shall be a list of variable parameters.

formal-parameter-list = '(' formal-parameter-section { ';' formal-parameter-section } ')' .

formal-parameter-section > value-parameter-specification ½ variable-parameter-specification

½ procedural-parameter-specification ½ functional-parameter-specification .

NOTE --- 1 There is also a syntax rule for formal-parameter-section in 6.6.3.7.1.

value-parameter-specification = identifier-list ': ' type-identifier .

variable-parameter-specification = 'var' identifier-list ':' type-identifier .

procedural-parameter-specification = procedure-heading .

functional-parameter-specification = function-heading .

An identifier defined to be a parameter-identifier for the region that is the formal-parameter-list of a procedure-heading shall be designated a formal-parameter of the block of the procedure-block, if any, associated with the identifier of the procedure-heading. An identifier defined to be a parameter-identifier for the region that is the formal-parameter-list of a function-heading shall be designated a formal-parameter of the block of the function-block, if any, associated with the identifier of the function-heading.

The occurrence of an identifier in the identifier-list of a value-parameter-specification or a variable-parameter-specification shall constitute its defining-point as a parameter-identifier for the region that is the formal-parameter-list closest-containing it, and its defining-point as the associated variable-identifier for the region that is the block, if any, of which it is a formal-parameter.

The occurrence of the identifier of a procedure-heading in a procedural-parameter-specification shall constitute its defining-point as a parameter-identifier for the region that is the formal-parameter-list closest-containing it, and its defining-point as the associated procedure-identifier for the region that is the block, if any, of which it is a formal-parameter.

The occurrence of the identifier of a function-heading in a functional-parameter-specification shall constitute its defining-point as a parameter-identifier for the region that is the formal-parameter-list closest-containing it, and its defining-point as the associated function-identifier for the region that is the block, if any, of which it is a formal-parameter.

NOTE --- 2 If the formal-parameter-list is contained in a procedural-parameter-specification or a functional-parameter-specification, there is no corresponding procedure-block or function-block.

Value parameters

The formal-parameter and its associated variable-identifier shall denote the same variable. The formal-parameter shall possess the type denoted by the type-identifier of the value-parameter-specification. The type possessed by the formal-parameter shall be one that is permitted as the component-type of a file-type (see 6.4.3.5). The actual-parameter (see 6.7.3 and 6.8.2.3) shall be an expression whose value is assignment-compatible with the type possessed by the formal-parameter. The current value of the expression shall be attributed upon activation of the block to the variable that is denoted by the formal-parameter.

Date: 2015-12-24; view: 870