Go to the first , previous , next , last section, table of contents . A primitive function is a function callable from Lisp but written in the C programming language. Primitive functions are also called subrs or built-in functions .
Most primitive functions evaluate all their arguments when they are called.
It does not matter to the caller of a function whether the function is primitive. However, this does matter if you try to redefine a primitive with a function written in Lisp. The reason is that the primitive function may be called directly from C code. Calls to the redefined function from Lisp will use the new definition, but calls from C code may still use the built-in definition. Therefore, we discourage redefinition of primitive functions .