A constant is any symbol that has been defined as such with the assignment operator ::=. Note that since the check is made at run-time, the constant is protected, even if the symbol name is evaluated at run-time.

Example:

Gamma> e ::= 2.17128128;
2.17128128
Gamma> e = 3;
Assignment to constant symbol: e
debug 1>

(Type Ctrl - D to return to
the Gamma prompt.)

Gamma>