Models 707B and 708B Switching Matrix Reference Manual
Section 6: Instrument programming
707B-901-01 Rev. A / August 2010
6-17
Values and variable types
In Lua, you use variables to store values in the runtime environment for later use.
Lua is a dynamically typed language; the type of the variable is determined by the value that is
assigned to the variable.
Variables in Lua are assumed to be global unless they are explicitly declared to be local. A global
variable is accessible by all commands. Global variables do not exist until they have been used.
NOTE
Do not create variable names that are the same as the base names of Model 707B or 708B
Instrument Control Library (ICL) commands. Doing so will result in the loss of use of those
commands. For example, if you send the command
digio = 5
, you cannot access the
digio.*
commands until the power to the instrument is turned off and then back on.
Variables can be one of the following types.
Variable types and values
Variable type
Value
Notes
nil
not declared
Nil is the type of the value
nil
, whose main property is to
be different from any other value; usually it represents the
absence of a useful value.
boolean
true or false
Boolean is the type of the values
false
and
true
. In
Lua, both
nil
and
false
make a condition
false
; any
other value makes it
true
.
number
number
All numbers are real numbers; there is no distinction
between integers and floating-point numbers.
string
sequence of words or characters
function
a block of code
Functions can carry out a task or compute and return
values.
table
an array
New tables are created with {} braces. For example,
{1, 2, 3.00e0}.
To determine the type of a variable, you can call the
type()
function, as shown in the examples
below.
Example: Nil
Code Output
x = nil
print(x, type(x))
nil nil
