exists

Test for the existance of a variable.

Syntax

status = exists ( variable ) ;

Arguments

list variable

• A valid identifier.

Return Value

boolean status

• 1

  The variable exists.

  The STATUS variable is set to $ACKNOWLEDGE

• 0

  The variable does not exist.

  The STATUS variable is set to %UNDEFINED

Warnings

%UNDEFINED : The variable does not exist.

Exceptions

%ARGUMENT : Invalid arguments. Usage: status = exists ( variable ) ;

%IDENTIFIER : 'variable' argument is not a valid identifier, literal, or reference

Description

Hyperscript variables can be defined and undefined on-the-fly, therefore it is often necessary to test for the existance of a variable. If the scope is local, the exists() function first tests for the existance of a a local definition of the variable before testing for a global definition.

Examples

To execute the example below, press or modify the example to try different variations. global ; int a = 100 ; if ( exists ( a ) ) describe a ; if ( !exists ( b ) ) puts "No variable named 'b'" ; // Switch to local scope local ; { // define a local definiton of a int a = 99 ; put a ; // delete the local definition undef a ; put a ; if ( exists ( a ) ) puts "Global definition of 'a' still exists." ; }

Related Links

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