[pjmlp]

Lisp 1.5 manual, appendix D, compiler

https://softwarepreservation.computerhistory.org/LISP/book/L...

"When the compiler is called upon to compile a function, it looks for an EXPR or FEXPR on the property list of the function name. The compiler then translates this S-expression into an S-expression that represents a subroutine in the LISP Assembly Language (LAP). LAP then proceeds to assemble this program into binary program space. Thus an EXPR, or an FEXPR, has been changed to a SUBR or an FSUBR, respectively. Experience has shown that compiled programs run anywhere from 10 to 100 times as fast as interpreted programs, the time depending upon the nature of the program. Compiled programs are also more economical with memory than their corresponding S-expressions, taking only from 50 per cent to 80 per cent a s much space.' The major part of the compiler is a translator or function from the S-expression function notation into the assembly language, LAP. The only reasons why the compiler is regarded as a pseudo-function are that it calls LAP, and it removes EXPRts and FEXPR1s when it has finished compiling."

Enough said.