Symbols

Symbols are implemented as a unique, non-modifiable UTF-8 string. ‘nil is a special symbol that is also a cons cell and the false boolean value. ’t is another preset symbol, the traditional true boolean (although anything different to ’nil is true). These two symbols should not be reset (that’s a bug, you are not allowed to do it, even if the compiler does not complain yet).

Functions implemented for symbols are is, isnt, pr, prn.