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constant
Combined from primary sources listed below.

In Variables§

See primary documentation in context for The constant prefix

The constant prefix declares that the value it tags is not going to change during its lifetime.

constant $pi2 = pi * 2;
$pi2 = 6; # OUTPUT: «(exit code 1) Cannot assign to an immutable value␤ 

The value is assigned at compile time. Since Raku modules are precompiled automatically, constants defined in modules are not re-evaluated when the program is run. Please check the section on constants in the Terms page for additional information.