Accessor VOPs

These VOPs read the global symbol value and definition cells. constant-ref may only be used on symbols that have been defined to be constants. Since a constant cannot change in value and cannot be dynamically bound, the compiler may be able to compile uses of constant-ref more efficiently. Unsafe versions of these VOPs may not check for the slot being unbound, which the corresponding functions are required to do.
\begin{example} {small, fast} symbol-value (symbol) => value {small, fast} const... ... (symbol) => value {small, fast} symbol-function (symbol) => value \end{example}

These VOPs set the global symbol value and definition cells. makunbound and fmakunbound are implemented by setting the value to the unbound marker.
\begin{example} {small, fast} set-symbol-value (symbol new-value) {small, fast} set-symbol-function (symbol new-value) \end{example}

The accessors for other symbol slots are translated into uses of the slot-ref and slot-set VOPs.