Boolean enumeration

The Boolean enumeration implements the standard logical paradigm of "true" and "false".

While, in some sense, it is just like any other enumeration, because the concept of true and false is so basic to programming, Boolean variables are treated specially by User Language.

Boolean enumeration values

The system Boolean enumeration values are:

• True
• False

However, like all other enumerations, a Boolean variable can also be unset so have a null value. While this can be useful in detecting references to unset variables, it can also be problematic in certain sitiuations. Use of the Initial clause on variable declarations and the Default clause on method parameter declarations can mitigate most of these issues, nevertheless it is important to keep in mind the possibility of a Boolean variable being null.

Declaring boolean variables

Boolean variables can be declared the same way any enumeration variables are declared, with the keyword Enumeration followed by the class name:

%truth is enumeration boolean

However, because boolean processing is such a basic part of any programming language, Boolean variables can be declared without the Enumeration keyword:

%truth is boolean

This is also true for method variables and results. For example, then following:

function foo(%n is float, %test is enumeration boolean) - is enumeration boolean

is identical to

function foo(%n is float, %test is boolean) is boolean

Many methods, for example the XmlDoc API Exists function, return a Boolean enumeration.

Unlike other Janus SOAP ULI enumerations, Boolean enumeration values are usable as the condition in an If statement:

%recset is object recordSet in file sirfiled ... find records to %recset rectype = 'FILE' end find ... if %recset:isEmpty then print 'No records found!' end if

In the above example, the IsEmpty method returns a Boolean enumeration value. Strictly speaking, the If clause expects a numeric zero or non-zero value as its operand, but in this context Janus SOAP ULI automatically converts a True to a 1 and a False to a 0.

Other places where a Boolean value can be used, that is, where it is automatically converted to the 0 or 1 that User Language expects are:

• As a Repeat statement operand.
• As an operand for a logical operator such as Not, And, or Or. This would usually be in an If or Repeat statement.

You can also use Boolean literals in these contexts, but they must be completely qualified as Booleans: otherwise there is a syntactic ambiguity between the values True or False and fields by the name of True or False. The following is syntactically valid:

if %(boolean):true then print 'Truth be told' end if

Besides the common enumeration methods, the system Boolean enumeration has additional methods available, which are described in the following sections.

IsFalse function

This function examines a Boolean enumeration and returns an integer (0 or 1) according to the Boolean value (True or False).

IsFalse syntax

%num = bool:IsFalse

Syntax terms

%num	If specified, a number variable that is assigned the value 0 if the value of bool isTrue, and 1 if bool is False.
bool	A Boolean enumeration variable or an expression that results in a Boolean enumeration.

IsTrue function

This function examines a Boolean enumeration and returns an integer (1 or 0) according to the Boolean value (True or False).

IsTrue syntax

%num = bool:IsTrue

Syntax terms

%num	If specified, a number variable that is assigned the value 1 if the value of bool isTrue, and 0 if bool is False.
bool	A Boolean enumeration variable or an expression that results in a Boolean enumeration.