Constants work differently to variables in the sense that they can only be
declared once. As of version 1.6.4, constants are defined
using the define
keyword:
define a = "Hello world"
Constants are then accessed by using the name of the constant:
$x = a
Predefined constants
ZPE provides several built in constants that can be accessed using their names:
| Constant name | Purpose | Value | Version added |
|---|---|---|---|
| Compile time constants | |||
PI
|
The value of π | 3.141592653589793 | 1.3.3 |
PLANCK
|
The value of Planck's constant | 6.62606957-34 | 1.3.3 |
LIGHT_SPEED
|
The value of the speed of light | 2.997924588 | 1.3.3 |
COULOMB_CONSTANT
|
The value of Coulomb's Constant | 8.9875517879 | 1.3.3 |
EULER_NUMBER
|
The value of Euler's number | 2.7182818285 | 1.3.3 |
GRAVITATIONAL_CONSTANT
|
The gravitational constant | 6.67408-11 | 1.7.5 |
ATOMIC_MASS
|
The atomic mass constant | 1.6627 | 1.7.5 |
GOLDEN_RATIO
|
The value of the Golden Ratio | 1.6180339887498948482 | 1.7.5 |
| Execution time constants | |||
ZPE_VERSION_MAJOR
|
The major version number of the ZPE instance used to compile the script. | Varies | 1.3.6 |
ZPE_VERSION_MINOR
|
The minor version number of the ZPE instance used to compile the script. | 1.3.6 | |
ZPE_CLI_VERSION
|
The CLI version number of the ZPE instance used to compile the script. | 1.3.6 | |
All constants are compiled are translated to their values at compile time unless they are specified as execution constants. This change came around with version 1.12.6.
Prior to version 1.12.6
From version 1.7.2 to version 1.12.5, all constants were compiled at runtime.
From version 1.7.2 the way constants work was completely rewritten and made them very different from variables in the way they work as they are compiled at compile time into their values. For example:
$x = PI
Since constants can be changed from the configuration file, it is possible to change, say, the value of the PI constant. If this program was compiled and distributed, the value of the PI constant would be set to what the value of PI was when the program was compiled and would not not change to the user's version specified in their configuration file.
Prior to version 1.7.2
Prior to ZPE 1.7.2, constants were accessed using the name of the constant
preceded by a # symbol:
$x = #a
Prior to version 1.6.4, the constant was assigned in the same way it is accessed:
#a = 51 $x = #a
