Constant

A constant is an identifier that is mapped to a numeric or a boolean value. All constants are case-sensitive and their value is immutable, i.e., their value cannot be changed after an expression has been parsed (Parser::parse()). A valid constant name conforms to PHP's constant expression definition:

A valid constant name starts with a letter or underscore, followed by any number of letters, numbers, or underscores.

Constant Definition

A constant may be registered for a given parser before expressions are parsed by invoking ConstantRegistry::registerLabel().

$registry = $parser->constant_registry;
$registry->registerLabel("myconstant", 10);

$parser->parse("myconstant * 2")->evaluate(); // 20
$parser->parse("min(myconstant, 12)")->evaluate(); // 10

A constant must be mapped to a value of the type int|float|bool). Unlike functions, resolving a constant's value does not involve any computation.

List of pre-defined constants

Constant	Value
e	2.718281828459
euler	0.57721566490153
false	false
inf	INF
log2e	1.442695040889
log10e	0.43429448190325
ln2	0.69314718055995
ln10	2.302585092994
lnpi	1.1447298858494
pi	3.1415926535898
nan	NAN
pi2	1.5707963267949
pi4	0.78539816339745
m_1pi	0.31830988618379
m_2pi	0.63661977236758
m_2sqrtpi	1.1283791670955
sqrtpi	1.7724538509055
sqrt2	1.4142135623731
sqrt3	1.7320508075689
sqrt12	0.70710678118655
true	true